Anand v Carlsen, Chennai 2013, game 9: one blocking move

Magnus Carlsen led the world champion, Viswanathan Anand, by two points going into game 9 of their 2013 world championship match in Chennai, played on 21 November. Anand switched to 1.d4 and a sharp line against Carlsen's Nimzo-Indian, saying he needed to change the course of the match. Carlsen said afterwards that it was the first time in the match he had been scared. Anand lost, Carlsen led 6–3, and a draw in game 10 made him world champion.

White to move after 27...b1=Q+. One move holds the balance.

The whole game

Anand v Carlsen, World Championship 2013, game 9. Step through all 28 moves; White resigned.

Anand's pawns go forward on the kingside, towards Carlsen's king; Carlsen's go forward on the queenside, towards a new queen.

What Stockfish makes of it

We had Stockfish check every move. It agrees with the commentators that the game was extremely complicated and close to level almost to the end.

20.axb4: a sharper path missed

Hikaru Nakamura thought 20.axb4 was not in the spirit of the position and that 20.f5 was a much stronger attacking move. Stockfish agrees that 20.f5 was better, though only by about half a pawn.

26...b2 and 27...b1=Q+

26...b2 27.Rf4 b1=Q+: Black queens with check.

With White's queen on h6 and pawns on f6 and g5, Black's king is in danger, but Black's b-pawn is faster. 26...b2 and 27...b1=Q+ were each the only move that held the balance for Black.

28.Nf1: the wrong piece

28.Nf1 Qe1: White resigned.

White has to block the check on the first rank. 28.Bf1 would have held: ChessBase's commentary gave 28...Qd1 29.Rh4 Qh5 as probably a draw, and Stockfish rates the position level. Anand blocked with the knight instead, 28.Nf1, and the knight had just been guarding h4 from g3. After 28...Qe1, the only winning move, Black wins White's rook on h4 and is a rook up: Stockfish rates Black more than three pawns better. Anand resigned. He said that as soon as he put the knight on f1 he realised what he had done.

How we checked

The moves are from Wikipedia's page on the 2013 World Championship and ChessBase, which agree. 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 history and the named opinions are from Wikipedia, ChessBase and Chess.com.

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