Endgame riddle: Fat Fritz knows more

by Karsten Müller
8/21/2020 – A while ago Karsten Müller asked ChessBase readers whether the adjourned position of the crucial sixth game of the Fischer-Petrosian Candidates match of 1971 in Buenos Aires was indeed a draw. Fischer won the game and the match, and one year later became World Champion, but our readers came to the conclusion that Petrosian could have drawn. However, in a crucial line Fat Fritz saw deeper.

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Petrosian vs Fischer revisited

The background of the question was described in our article "Could Petrosian have held against Fischer?" The critical game took place in Buenos Aires, Argentina. As a candidate for the World Championship Bobby Fischer had demolished two of the world's strongest grandmasters in the quarter and semifinals: he defeated Mark Taimanov and then Bent Larsen with perfect 6-0 scores. Now he faced former World Champion Tigran Petrosian, whose defensive skills many though would be Fischer's stumbling block.

The match started badly for Fischer, who was probably suffering from a cold and could not sleep in the noisy hotel. After five games the score was 2½-2½, and Petrosian arrived for game six looking relaxed and confident, while Fischer was pale and exhausted. The game, a tense battle, was adjourned after move 41, with Petrosian sealing the move.

In the above image, left, Fischer has just played 41..Kc5-b5. In the image on the right (and on our front page in colour), Petrosian is in the process of sealing his move

Fischer went on to win this game and he also won games 7, 8 and 9, ending the match with 6½-2½ points. But leading endgame expert GM Karsten Müller asked: "Should we assume that the adjourned position before the sealed move is a draw (as most sources and analysts do)? Then where did Petrosian go wrong in the game – or did Fischer perhaps also go wrong later, and Petrosian then made another mistake?"

Readers were asked to send analysis to Karsten Müller, who would evaluate all contributions and would show us what his own analysis had revealed – so far.

After evaluating the many contributions came to the conclusion that the adjourned position was indeed a draw: https://en.chessbase.com/post/petrosian-could-have-held

But Fat Fritz disagrees. Albert Silver, who currently works on a new version of Fat Fritz (Fat Fritz 2 Beta) indicated that the NN engine has found a mistake in the published solution.

Here is Karsten's improved analysis, including the findings of Fat Fritz 2 Beta.


Actually, this is the fist time that a mistake was found in the published solution of the endgame riddles – and it took a powerful and very modern engine to find this mistake. Probably, in the future Fat Fritz will improve other endgames as well.


Karsten Müller, born 1970, has a world-wide reputation as one of the greatest endgame experts. He has, together with Frank Lamprecht, written a book on the subject: “Fundamental Chess Endgames” in addition to other contributions such as his column on the website ChessCafe as well as in ChessBase Magazine. Müller's ChessBase-DVDs about endgames in Fritztrainer-Format are bestsellers. The PhD in mathematics lives in Hamburg, where he has also been hunting down points for the HSK in the Bundesliga for many years.


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