Great Moments in Sicilian ...d5 Theory

The diagram, a followup to my recent post ECO B33 & B44, illustrates a couple of famous and surprising Sicilian ...d5 moves that occurred in world class matches. On the left is a position from game one of Fischer - Petrosian, 1971 Candidates Final; on the right is game 16 of Karpov - Kasparov, World Championship 1985. What finally became of these two variations, which kept chess analysts busy around the world in the months after they were played?

The initial moves of Fischer - Petrosian were 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nc6 5.Nb5 d6 6.Bf4 e5 7.Be3 Nf6 8.Bg5 Be6 9.N1c3 a6 10.Bxf6 gxf6 11.Na3 d5. The position after 11.Na3 had been analyzed by Fischer in '60 Memorable Games' (no.54, Fischer - Najdorf, 1966 Santa Monica), where he gave 8...Be6 a '?' and concluded that Najdorf's 11...Nd4 was no better than Black's alternatives 'all favoring White'. In the 1971 game, Petrosian inexplicably varied from his home preparation, failed to play the best line, and lost a game he could have won.

The initial moves of Karpov - Kasparov were 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 Nc6 5.Nb5 d6 6.c4 Nf6 7.N1c3 a6 8.Na3 d5. The same moves had been seen in the 12th game, which ended in an 18-move draw. During the week and a half between that game and the 16th, Karpov and his assistants had time to analyze 8...d5, but Kasparov, showing confidence in his own analysis, did not hesitate to repeat it. He won one of the best games of his illustrious career, as well as one of the most important. It was the turning point in the match which brought him the title of World Champion.

To play through the complete games see...

Robert James Fischer vs Tigran Vartanovich Petrosian, Buenos Aires cf 1971
http://www.chessgames.com/perl/chessgame?gid=1044350

...and...

Anatoli Karpov vs Garry Kasparov, World Championship Match 1985
http://www.chessgames.com/perl/chessgame?gid=1067175

...on Chessgames.com. What was the ultimate fate of the two variations? Petrosian's move held up to the test of time, and Fischer's 9.N1c3 has been replaced by 9.Nd2. Kasparov's move was refuted a few months later by Karpov himself: 9.cxd5 exd5 10.exd5 Nb4 11.Be2 Bc5, and now not 12.O-O, but 12.Be3 Bxe3 13.Qa4! (Karpov - Van der Wiel, Brussels 1986). It was one of the rare cases where Kasparov's preparation later proved to be faulty.