Continuing with Keres - Fischer, CT 1959, after 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 (Fischer's favorite Najdorf variation) 6.Bg5 e6 7.f4 Be7 8.Qf3 Qc7 9.O-O-O Nbd7, the 'bait' in Fischer Takes the Bait was 10.Be2 b5 11.Bxf6 Nxf6 12.e5 Bb7, reaching the diagrammed position.
1959 Candidates Tournament (round 1)
[FEN "r3k2r/1bq1bppp/p2ppn2/1p2P3/3N1P2/2N2Q2/PPP1B1PP/2KR3R w kq - 0 13"]
Keres played the surprising 13.exf6, sacrificing the Queen. Fischer again took the bait with 13...Bxf3 14.Bxf3 Bxf6 15.Bxa8 d5 (trapping the Bishop behind enemy lines) 16.Bxd5 Bxd4 17.Rxd4 exd5.
Here Fischer wrote nothing about White's next move 18.Nxd5, but Kasparov mentioned an important alternative.
In the tournament book Ragozin recommended 18.Re1+ Kf8 19.Re5 'as the most advantageous for White', giving the variation 19...h5 20.Rexd5 Kg8 21.Rd7 Qc6 22.Ne4. But after 20...g6 Black successfully defends: 21.Rd7 Qc6 22.Ne4 Kg7 23.Ng5 Rf8. And the immediate 19...g6 20.Nxd5 Qc6 followed by 21...Kg7 is even better.
The idea 18.Re1+ Kf8 19.Re5 was tested in many subsequent games. Although Kasparov's 20...Qc6 was never played, the similar 20...Qd6 was tried in Richardson - Zagorovsky, 7th World Correspondence Championship, in the mid-1970s. Zagorovsky won.
Fischer also dismissed 13.Qg3 (instead of 13.exf6) with 13...dxe5 14.fxe5 Nd7 15.Qxg7 Qxe5, and 'Black stands better'. After 14...Nd7, the critical moves are 15.Bxb5 and 15.Bf3. Both moves were successfully employed by Juan Morgado in the 1970s and 1980s at the highest levels of correspondence chess, including the 10th World Correspondence Championship, where Morgado finished second. Correspondence chess is often the ultimate testing ground for razor sharp variations.