Carlsen - Anand, Game 6 : Carlsen's Blunder

After Carlsen - Anand, Game 6 : The Opening, the players eventually reached the position shown in the diagram. In fact, they reached the position twice. After 23...a5, White spent two moves shuttling the light-squared Bishop to d1 and back to c2, while Black marked time moving the Rook to d8 and back.

After 23...a6-a5 & 25...Rd8-g8

On the second appearance of the position, Carlsen played a move which will be remembered for as long as World Championship matches are discussed.

• 26.Kd2?? Followed by Anand's equally outrageous 26...a4??; the move 26...Nxe5 should win easily

During the press conference, both players said they saw their own blunder just after playing the move and punching the clock. Asked, 'Did this blunder influence your game afterwards?', they replied,

Carlsen: For me, my play wasn't that confident. I didn't feel that I found the right setup. So, yes, I guess it affected me to some extent. • Anand: Given the way I played the rest of the game, probably.

The diagrammed position is complicated and full of dynamics. What should Carlsen have played instead? During the press conference he mentioned,

• 26.Kd1, indicating the same continuation as in the game, 26...a4 27.Ke2; here Black has the much better move 26...Nf8, when White loses the Pawn on g2.

Captures on g6 and h6 are problematic for various reasons.

• 26.Rxh6? Nxe5
• 26.Bxg6?! Rxg6
• 26.Bxh6!? walks into a pin on the h-file; Black can continue 26...Kc8 or 26...Ka6, with the threat 27...Ne7, and good counterplay against White's Kingside Pawns

What did the commentators suggest? On the first occurrence of the position, they looked at 24.Bxh6. Then when the position was repeated for move 26, they decided to take a break. During the break the blunders occurred, and because the live video feed was also turned off, the reactions of the two players were not recorded. Let's call it 'the infamous seven minute gap'.

What do the engines suggest? A couple of non-committal moves, like Carlsen's first choice, 24.Bd1 (26.Bd1), score well.

• 26.Rg3 and 26.Bd2

Perhaps the best move is more concrete and committal. It closes the diagonal to Black's Bishop, protects the Rook on g4, and puts the ball back in Black's court.

• 26.f3, followed by Anand's 26...a4, or maybe a Knight move (26...Ne7, 26...Nf8).

While I was preparing this post, I didn't have time to see what the GM annotators have suggested. Along with the double blunder, the position will likely be discussed for as long as people are interested in chess.