|DrGridlock: Game is included in Palliser's "The Modern Benoni" under "The Modern Benoni Endgame." Palliser writes,|
"Speaking of a typical Modern Benoni ending is far from easy. Usually one side will have already triumphed or gained a large advantage by then: either White will have crashed through or come undone on one of the flanks. One side may also have come unstuck in the middlegame complications. However, it is not unknown that the game can also remain very complex right into the endgame."
While black has an advantage after move 37 Qc5, Palliser writes,
"White had probably been relying on this, while Tal probably wasn't worried by it. As his a-pawn goes west Black can quickly push his b-pawn if necessary, but even more important is the relative strength of the minor pieces. Even with few pieces left, Black's queen and knight combine well, while the White bishop remains rather locked out of the game even with the board fairly open. However knights usually like Benoni endings if the position is still quite blocked."
The position after move 38 is crucial:
Arshak B Petrosian - Mikhail Tal
click for larger view
After White's 39 Qa6, Palliser writes,
"Essential to save the exchange and to prevent the other threat - which would have been easy to overlook in time trouble - of 39 ... Nxc6."
What Palliser (and likely Tal and Petrosian) missed was that after 39 Qxb4 White loses the exchange (for two pawns), but completely equalizes. Komodo scores it:
39 Qxb4 Nf3+
40 Kh1 Nxe1
After the game continuation, Qa6, Black rolls to a smooth victory.
Pallister (and likely Tal and Petrosian) were focused on White avoiding losing the exchange, but that is precisely the path to White saving a half point in the game.