My human thinking was the straight forward 18.Bxc3 putting the Queen on guard. Komodo 9.02 likes 18.Qc4. Fischer's move 18.Rf5 turns out to be the best see the analysis below.
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3r1r1k/p3bPpp/2bp1n2/q7/3BP3/1Bp5/PPP1Q1PP/1K1R1R2 w - - 0 1
3r1r1k/p3bPpp/2bp4/5R2/1q1Bn3/1Bp5/PPP3PP/1K1R1Q2 w - - 0 20
Maybe the real mistake of Fischer is 20.a3 after which Geller's queen moves to b7 indirectly hitting Pf7 and over protecting Ne4. Not only that, white's Bb3 is weakened by this move, and as you saw 21. ... Ba4 settled the game.
Can you guess the only move in this variation (According to this laptop)?
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3r1r1k/p3bPpp/2bp1n2/7R/1q1B1Q2/1B6/PpP3PP/1K1R4 w - - 0 22
Interesting positional study! It appears Fischer has a positional advantage but he cannot find a continuation. After 21. Rh5! Houdini analyzes the game to equality or slightly better for white. Unfortunately, Fischer plays 21. Qf4?
3r1r1k/pq2bPpp/2bp4/5R2/3Bn3/PBp5/1PP3PP/1K1R1Q2 w - - 1 21
Hi, thanks for posting. May I inquire why you are using "old" chess engines for your analysis?
Sean
Hello Sean,
Old? Chess Challenger is an “old” engine. Would it make any difference to the outcome using the latest version of Komodo with 16 threads? There is little use in comparing a 3400 rated machine against the moves of any human opponent. It is difficult keeping up with all the latest compilers, tools and engine versions, but Stockfish could be updated. It is already good enough to beat me in chess. Maybe I am nostalgic.
The answer to your question is that the move 21 Fischer-Geller position is a favorite of mine, and the analysis was made some time ago.