Brazil's round 6 opponents at the Olympiad: how Belgium and Paraguay play

Short answer

In round 6 of the 46th Chess Olympiad, on 21 September 2026, Brazil face Belgium in the open section on board 18 and Paraguay in the women's section on board 30. Drawing on 417 classical games broadcast by Lichess over the last three years, this article sets out each player's repertoire by colour, the lines where each of them scores below their own average, where the engine finds the mistakes, and what the online repertoire adds — always with the number of games beside every percentage, because that is what says how much of the dossier holds.

Event: 46th FIDE Chess Olympiad

How this was compiled: Compiled on 20 September 2026, with round 5 finished and round 6 not yet played: it starts on 21 September at 3pm Samarkand time (10:00 UTC). The pairings were checked on chess-results; the official PGN that names each team's line-up is only published when the round starts, so this dossier covers both full squads rather than four boards each. The repertoire uses the 417 over-the-board classical games from the last three years broadcast by Lichess and linked to each player by FIDE ID — 289 for the Belgian squad and 128 for the Paraguayan one. The mistake profile measures each player's 12 most recent games with Stockfish 19 at depth 16; for Helen Montiel it was 10, because two games failed to parse and are recorded as failures. Every move quoted in this text was re-measured at depth 24, with a dedicated search and a cleared hash. The blitz and rapid repertoire comes from verified Chess.com accounts, over a 90-day window.

The essentials in a few lines

• In round 6, on 21 September 2026, Brazil face Belgium in the open section (board 18) and Paraguay in the women's section (board 30). Both matches are level on match points and Brazil is behind on the first tiebreak in each. Line-ups are only published when the round starts, so this dossier covers all ten players in the two opposing squads.
• Belgium is two teams in one. Elias Ruzhansky opened 1.e4 in all 46 of his White games in the sample and Thibaut Vandenbussche in all 31 of his — 100% for both. Sim Maerevoet and Mikhail Gurevich never opened 1.e4 once: they play 1.d4, 1.c4 and 1.Nf3.
• Mikhail Gurevich, at 67, scores 84.4% with White in the 16 games of the sample, without a single loss. It is the best White figure in either squad, and it comes from the second-smallest Belgian sample.
• Three of the five Paraguayans score better with Black than with White — Renata Mayeregger 75.0% in 14 against 55.0% in 10, Gabriela Vargas 70.0% in 10 against 53.3% in 15. The inversion belongs to the team, not to one player.
• The engine confirmed two real mistakes on the Belgian side, both in positions that changed result: Ruzhansky went from dead level to −10.8 in an endgame against Syria and drew anyway; Vandenbussche dropped +10.2 in a Belgian open and drew. Neither is the move a shallow reading would have flagged.

The round 6 picture

Brazil arrive at round six after beating Ireland 2.5–1.5 in the open section and losing 1–3 to Hungary in the women's. Both of the new matches repeat a shape that already appeared last round: the teams level on match points and Brazil behind on the first tiebreak. In the open, Brazil and Belgium both have 7 match points, and Belgium leads on game points, 12.5 to 11. In the women's, Brazil and Paraguay both have 6, and Paraguay leads 15 to 13.

On rating Brazil is the favourite in both. It is the 31st seed in the open facing the 46th, and the 44th in the women's facing the 76th. The distance between the seeding and the table is what a Swiss system produces after five rounds: it pairs teams that have scored the same, not teams that look alike. Belgium got here by drawing 2–2 with Iran in round 3 and losing 1–3 to Georgia in round 4; Paraguay alternated four whitewashes with two narrow defeats, to Sweden and Croatia, both 1.5–2.5.

The sample column in the table below says how much of each dossier holds. Sim Maerevoet has 106 classical games broadcast in three years, the largest of the match; Arben Dardha has 6, and is the only one of the ten the dossier flags as low confidence. No weak lines and no game plan are published for him here, for an arithmetic reason: with three games per colour, any percentage is noise. That is 417 games in total, 289 Belgian and 128 Paraguayan.

None of the ten played all five rounds. Gurevich came in for rounds 1, 2 and 5; Maerevoet from round 2 to round 5; Helen Montiel only from round 3. Olympiad teams rotate their squads, which is why the dossier covers five players a side rather than guessing four.

Belgium: two repertoires inside the same team

Knowing which move comes first is the cheapest part of preparation and one of the most productive, and here it separates the team into two blocks. Ruzhansky opened 1.e4 in the 46 White games he has in the sample, and Vandenbussche in his 31. This is not 'almost always': it is everything that was broadcast in three years. On the other side, Maerevoet spreads his 54 White games between 1.d4, 1.Nf3 and 1.c4, and Gurevich does the same with his 16. Which of them Brazil meets on each board changes the preparation entirely, and that will only be known when the round starts.

Elias Ruzhansky, Belgium's second board in the rounds he has played, is the squad's great drawer: 22 draws in 46 White games and 18 in 42 with Black. His 60.9% with White comes from 17 wins and 7 losses across those 46 — the profile of somebody who rarely loses and rarely overwhelms. Against him the dossier points at the French: with White, after 1.e4 e6, he scores 54.5% in 11 games against his own 60.9% average. That is six percentage points over eleven games, a medium-confidence indication rather than a settled plan. The line 1.e4 c5 2.Nf3 Nc6 gave him 33.3% in 3, and three games support no recommendation at all.

Thibaut Vandenbussche is the most balanced between colours, 62.9% with White and 59.7% with Black, and he carries the Belgian squad's most reliable edge: against the Sicilian with 2...d6 he scores 50.0% in 6 games, nearly 13 points below his own White average. The same direction appears with 2...e6 (50.0% in 5) and against the French (50.0% in 3), which suggests the problem is not one variation but what happens when Black declines the open game he prefers. With Black he answers 1.e4 with 1...c5 in 16 of 31 games and scores 62.5% doing it — above his own average, so no edge there.

Mikhail Gurevich is the name any preparation recognises, and the dossier explains why he is still in the squad at 67. In the 16 White games of the sample he scored 11 wins, 5 draws and no losses — 84.4%, the best White figure in either match in this article. With Black he is at 63.6% in 11. The caveat is the usual one and deserves stating: 27 games in three years, the second-smallest sample in the squad, because he plays little broadcast classical chess. What the dossier records as a weak line for him is nothing at all: across 27 games there is no line with three repetitions and a ten-point drop.

Sim Maerevoet, with 106 games, is the best described of the squad and also the hardest to attack. He makes 65.7% with White and 61.5% with Black, and the two weak lines on record — 1.d4 Nf6 2.c4 e6 3.Nf3 and the Sicilian with 2...d6, both 50.0% in 3 games — have samples far too small to become a plan. Against him, what the dossier finds with White is 1.e4, at 59.3% across 27 games: below his 61.5% Black average by a margin that means nothing. He is a player with no visible hole, and saying so is as much preparation information as naming a line.

Arben Dardha, father of Daniel Dardha and the squad's fifth board, has 6 classical games broadcast in three years. The dossier flags low confidence, which is why this article publishes neither a repertoire nor a weak line for him. What six games allow is this: he played three with each colour and scored 50.0% with both — and that is close to nothing.

Paraguay: the Mayeregger sisters and a team that scores better with Black

The Paraguayan squad has two sisters, Fiorella Allegra and Renata Valentina Mayeregger, on boards 2 and 4 of the entry list, and five players separated by 223 rating points — from 2123 to 1900. The samples run from 14 to 33 games: none is low confidence by the dossier's standard, which starts flagging below 10, but none is large enough to support a strong claim about a specific variation either. Almost every weak line registered in this team has three or four games behind it.

The colour inversion is the squad's real finding. Renata Mayeregger scores 75.0% in 14 Black games and 55.0% in 10 with White; Gabriela Vargas, the squad's first board, makes 70.0% in 10 with Black and 53.3% in 15 with White; Fiorella Mayeregger sits at 65.6% and 62.5%, with 16 games each. Three players with the same shape is not a small-sample coincidence, it is a trait of the group: these are players who defend better than they attack, at least in what Lichess broadcast. Against them, the advantage of the first move is worth less than the rating suggests.

Helen Montiel is the most useful exception for Brazil, and the one with the squad's most reliable line. She scores 41.7% across 18 Black games, the team's worst figure with that colour, and inside it there is a specific point: against 1.e4 c5 2.Nf3 e6 she drops to 25.0% in 6 games, almost 17 points below her own average. It is the only medium-confidence weak line on the Paraguayan side. With White she is a different player, 60.0% in 15, and opens 1.d4 most of the time.

Paula Oviedo has the smallest sample in the squad, 14 games, and the widest distance between colours: 75.0% in 8 with White against 41.7% in 6 with Black. With six and eight games, though, that distance is more a question than an answer. What the dossier can say is that with White she showed up with the Sicilian Alapin twice, and that against her the first move with the best history for the player facing her is 1.e4 — 25.0% in 4 games, low confidence.

Gabriela Vargas plays the longest games of the ten players in this article: a median of 99 half-moves, with 84% of her games passing move 40. Whoever faces her should expect an endgame, and an endgame after the time control. It is the kind of information that never shows up in a repertoire and changes the preparation for the day: sleeping well matters more against her than memorising a variation.

Where the engine finds the mistakes

The table gives average evaluation loss per move in each phase, with the number of moves measured beside it. That second number matters as much as the first: 84 centipawns over 96 endgame moves and 23 over 33 describe different things, even though the column is the same. The opening column varies least within each team and most between them: 5 to 7 on the Belgian side, 8 to 14 on the Paraguayan. That is where preparation shows.

On the Belgian side, Sim Maerevoet has the cleanest profile — 15 in the middlegame and 19 in the endgame, over 210 and 185 moves — which fits a dossier with no exploitable edge. Thibaut Vandenbussche has the squad's most expensive middlegame, 31 over 201 moves, and its cheapest endgame, 17 over 97. Mikhail Gurevich is the opposite: 22 in the middlegame and 29 in the endgame, the latter over 298 moves, the largest endgame base in the match. He plays long endings, and pays a little for it.

The worst moment the depth-16 pass flagged in Gurevich was a king-and-pawn endgame against Bashir Eiti of Syria, in round 2 of this Olympiad, with a recorded loss of 970 centipawns. Re-measured at depth 24 the move is not a mistake: the position was mate in 13, he chose a line that mates in 12 rather than the one that mates in 9, and he won the game. It is the same artefact that appeared in round 5 of this series — in a decided position, a shallow pass charges fortunes for moves that change nothing.

The two mistakes that survived the check are of a different kind, and they stand out precisely because they look small in the shallow measurement. Against Mazen Fandi of Syria, in round 2 of the Olympiad, Elias Ruzhansky was dead level when he played 32.Rb1: the evaluation went from 0.00 to −10.77, because the rook on h1 had to be captured. He drew the game anyway. A month earlier, at the Geraardsbergen Open, Thibaut Vandenbussche was +10.15 against Chunhui Du and played 29.Nf4 instead of 29.Nxf6+: the evaluation collapsed to +0.07 and the game was drawn.

The pattern is worth recording, because it repeats every round of this series and runs against intuition: the worst moments carrying enormous depth-16 losses are nearly always artefacts of already-decided positions, while the mistakes that actually changed a result showed up with modest figures — 981 and 855 centipawns here. That is why no worst-moment number reaches this text without being re-measured at depth 24, with a dedicated search and a cleared hash.

On the Paraguayan side the two most expensive endgames belong to Paula Oviedo (84 over 96 moves) and Renata Mayeregger (65 over 185). Oviedo's three worst moments come from the same game, against Colombia at the 2024 Budapest Olympiad, and re-measuring dismantled the first two: at move 68 she played the engine's own first choice, and at move 65 she traded a mate in 15 for a position at +8.3, which no reasonable definition calls a mistake. The 84 describes a won game that took a while to finish. The same holds for Renata Mayeregger's figure, whose two worst moments are in positions already lost by nine pawns.

Blunder counts are deliberately absent from the table, for a methodological reason: the classification uses uncapped loss, so a winning player who picks a slower mate collects a blunder without having erred. Gurevich is exactly that case. Average centipawn loss caps each evaluation at 1000 and does not suffer from the same problem.

What the online accounts show, and what they do not

This section answers a different question from the one above, which is why it is kept separate. A blitz and rapid repertoire is usually wider than a classical one, and what somebody plays with three minutes is not what they prepare for a five-hour game. It tells you what they know, not what they will play tomorrow.

Sim Maerevoet is the only player in this match with a usable online sample: 44 games in 90 days on the account minisim, with an IM title verified by the platform. There he scores 54.3% with White in 23 games and 52.4% with Black in 21 — eleven points below his over-the-board figures in both colours. The interesting part is what that is not: it does not mean he plays worse, it means the opposition and the time control are different. The two lines the dossier marks there have three and four games, and support nothing.

Paula Oviedo has 15 games on the account dharichess, at 64.3% with White in 7 and 56.2% with Black in 8 — a small sample, reported as one. Helen Montiel has a single game in the window, and one game is not a sample. Mikhail Gurevich, Arben Dardha and Gabriela Vargas have verified accounts and no classical or rapid games in the period: the account exists and is idle, which is different from the account not existing.

Four opponents are absent from this section because no account could be verified: Elias Ruzhansky, Thibaut Vandenbussche and both Mayeregger sisters. None appears in Chess.com's titled-account index with a matching real name, and none has a Lichess profile with a verified title. A matching username is not verification, and publishing a stranger's repertoire under an athlete's name is worse than publishing nothing.

What to watch in round 6

The practical question in the open match is not which variation to play but who will be sitting there. If Belgium fields Ruzhansky and Vandenbussche on the top boards, Brazil faces two 1.e4 players whose White repertoire holds zero surprise on move one and known edges after it — the French against Ruzhansky, the Sicilian with 2...d6 against Vandenbussche. If it fields Maerevoet and Gurevich, opening preparation yields far less, and what remains is the mistake profile: Maerevoet barely errs, and Gurevich plays long endgames.

In the women's match, the figure Brazil can lean on hardest is Helen Montiel's against the Sicilian with 2...e6: 25.0% in 6 games, against her own 41.7% average with Black. Six games make that a strong indication, not a certainty. The warning from the other direction is the whole team scoring better with Black: whoever has White against Vargas or Renata Mayeregger will find a more comfortable opponent than the rating suggests, and a 70-versus-53 gap does not appear by chance in three players at once.

Once the round starts and the official PGN carries the line-ups, the dossier file attached to this article switches to showing the four boards and each board's game, with no change to the text. Until then, what is here is the full squad — which is what there is to prepare on the eve of a round.

Frequently asked questions

Update log

• 2026-09-20 — First publication, with the round 6 pairings checked on chess-results and the round not yet played: repertoire from the 417 classical games broadcast by Lichess, mistake profile with Stockfish 19 at depth 16, and the blitz and rapid repertoire of the verified accounts. The dossiers cover both full squads; once the line-ups are published, the same file will show the four boards and each board's game.
• 2026-09-29 — The Olympiad ended on 27 September: Uzbekistan won the open and China the women's event. This coverage is no longer updated; the final result is in the standings story.

Sources

• 46th Chess Olympiad Samarkand 2026, Open — round 6 pairings — Chess-Results
• 46th Chess Olympiad Samarkand 2026, Women — round 6 pairings — Chess-Results
• Sim Maerevoet — broadcasts under FIDE ID 241725 — Lichess
• Sim Maerevoet (minisim) — titled profile that verifies the account used for the online repertoire — Chess.com

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