Carlsen v Nepomniachtchi, 2021, game 6: 136 moves

Game 6 of the 2021 world championship match in Dubai, played on 3 December 2021, lasted 136 moves and about 7 hours 45 minutes, the longest game in the championship's history. It broke a run of 19 drawn classical games in title matches going back more than five years. Magnus Carlsen beat Ian Nepomniachtchi to lead 3½–2½; Nepomniachtchi blundered in three of the remaining games, and Carlsen won the match 7½–3½.

Black to move after 130.Kh3. The position is a draw with best play; 130...Qe6 loses.

The whole game

Carlsen v Nepomniachtchi, World Championship 2021, game 6. Step through all 136 moves; Black resigned.

What Stockfish makes of it

We had Stockfish check every move. For a game this long, it is worth separating what the engine says from what the endgame tablebases say: from move 115 there were only seven pieces on the board, where tablebases give the exact result, and the tablebase verdicts below are from Wikipedia's account. Stockfish's numbers in that stage are its own estimates.

Moves 29 to 40: chances missed on both sides

33.Rd1 Bxa3 34.Rxb5 Qd7 35.Rc5 e5 36.Rc2 Qd5: both players miss chances in time trouble.

Stockfish doesn't always agree with the annotations on Wikipedia. They mark 29...Be5 as inaccurate, saying 29...Bb2 would have drawn; Stockfish rates both moves the same, about level. They call 31...Bb2 a losing move; Stockfish calls it an inaccuracy, with Black under a pawn and a half worse.

Where Stockfish does agree: in time pressure Carlsen missed his winning chance with 33.Rd1, where 33.Rcc2 would have kept White more than a pawn better. Then 36...Qd5 missed 36...Bxb4, which would have given Black the better of it. And at move 40 Carlsen missed 40.Rdc2!!, which would have kept White more than one and a half pawns better; after 40.Nxe4 the game was level again.

52...Qe4 and the long defence

Black to move after 52.Kh2. 52...Qe4 gives the a-pawn for White's h-pawn.

Nepomniachtchi later said 52...Qe4 was unnecessary: it gave up his a-pawn for White's h-pawn and made the defence harder. Stockfish rates 52...Kg7 slightly better. Anish Giri called the position terribly unpleasant for Black but holdable, and Black held it for another 78 moves.

130...Qe6: the losing move

130...Qe6 131.Kh4 Qh6+ 132.Nh5 Qh7 133.e6 Qg6 134.Rf7 Kd8 135.f5 Qg1 136.Ng7: Black resigned.

According to the tablebases, the endgame was a draw until 130...Qe6; 130...Qc2 or 130...Qb1 would have held, and after 130...Qe6 White has a forced mate in 60. 133.e6! can't be met by taking the pawn, because of a royal fork with Ng7+. After 136.Ng7, White's king can reach g8, sheltered from the queen's checks, and the pawn will queen. Nepomniachtchi resigned.

How we checked

The moves are from Wikipedia's page on the game. We replayed every move with python-chess: all are legal.
The engine: Stockfish 16.1 checked every move at depth 22, and the key moments again at depth 26. "A pawn better" is Stockfish's measure of the position, not a count of material. The tablebase verdicts in the seven-piece ending are from the Wikipedia article; we didn't run tablebases ourselves.
The history and the named opinions (Nepomniachtchi, Giri, the move marks) are from the Wikipedia article.

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