WMD: <e4 e5 2. Nf3 Nc6 3.Bb5 a6 4. Ba4 Nf6 5. 0-0 Be7 6. Re1 b5 7. Bb3 d6 8. c3 0-0 9. h3 Bb7>GM Andy Soltis: "The real point lies in Black's next move, 10...Re8. For decades it was thought that Black could not move his Rook from f8 until he had disposed of White's possible reply Ng5!. It was to stop the Knight move that Smyslov had championed 9...h6 (and also 9...Qd7 so that he could meet a later Re8/Ng5 with ...Nd8!?).
10.d4 Re8
"Now on 11.Ng5 Black will simply retreat his Rook to f8. Efforts have been made to find something useful for White to do after 11.Ng5 Rf8 but 12.f4 exf4 13.Bxf4 appears too risky because of 13...Na5 14.Bc2 Nd5! attacking the f4-Bishop and g5-Knight.
"Before Igor Zaitsev introduced this wrinkle, 11...Rf8, in the mid-1970s it was believed that Black had to play something like 10...exd4 11.cxd4 Na5 12.Bc2 d5 with complications after the gambit continuation 13.e5 Ne4."
One drawback of the Zaitsev is that it practically allows White a draw by repetition if so desired:
Ng5-Rf8-Nf3-Re8-Ng5 etc.
The 1990 WC match between Kasparov and Karpov saw the discussion of the Zaitsev taken to its zenith. Karpov employed it in games 2, 4, 20 and 22, scoring =2 -2.
