better for White) 5.Qxd4 d5 6.exd6 Nxd6 7.Nc3 Nc6 8.Qf4 the game is approximately . After the other capture, 3...Nxe4, 4.Bd3 d5 (4...Nc6!? 5.Bxe4 d5, intending 6.Bd3 e4, is also possible) 5.Nxe5, when either 5...Nd7 or 5...Bd6 gives roughly equal chances. A long and complicated tactical sequence which has frequently been seen in master games is 3...Nxe4 4.Bd3 d5 5.Nxe5 Bd6 6.0-0 0-0 7.c4 Bxe5 8.dxe5 Nc6 9.cxd5 Qxd5 10.Qc2 Nb4 11.Bxe4 Nxc2 12.Bxd5 Bf5 13.g4 Bxg4 14.Be4 Nxa1 15.Bf4 f5 16.Bd5+ Kh8 17.Rc1 c6 18.Bg2 Rfd8 19.Nd2 (diagram) and White has the slightly better endgame after either 19...Rxd2 20.Bxd2 Rd8 21.Bc3 Rd1+ 22.Rxd1 Bxd1 or 19...h6 20.h4. Three Knights Game: 3.Nc3 3.Nc3 is the Three Knights Game of Petrov's Defence. It can also be reached via 2.Nc3 Nf6 3.Nf3 (the Vienna Game). Commonly, after 3...Nc6, the opening transposes to the Four Knights Game. With the reply 3...Bb4 (or some others), it remains the Three Knights Game proper. Italian Variation: 3.Bc4 3.Bc4 is the Italian Variation of Petrov's Defence. With 3...Nc6, it transposes to the Two Knights Defence. Boden–Kieseritzky Gambit Another possibility is 3.Bc4 Nxe4 4.Nc3, the Boden–Kieseritzky Gambit. It is not considered wholly sound, since Black has several viable options. Black can accept the gambit with 4...Nxc3 5.dxc3 f6, but must play carefully after 6.0-0 (for example 6...Bc5?? 7.Nxe5! is disastrous; 6...d6 and 6...Nc6 are good). Another more aggressive try is 6.Nh4, where White goes for a quick assault on Black's king, but Black can maintain a small advantage if he plays cautiously via 6...g6 7.f4 Qe7 8.f5 Qg7 9.Qg4 Kd8. Another possibility is returning the gambit pawn with 4...Nxc3 5.dxc3 c6 6.Nxe5 d5, which equalises. A third possibility is transposing to the Italian Four Knights Game with 4...Nc6, and if 5.Nxe4, 5...d5. If 5.Bxf7+?, then 5...Kxf7 6.Nxe4 d5 gives Black the and control of the . If 5.0-0, Black plays 5...Nxc3 6.dxc3 and now Black can play 6...Qe7!, after which Bobby Fischer wrote that "White has no compensation for the Pawn", or 6...f6 transposing to the main line of the Boden–Kieseritzky. Black also has lines beginning 6...Be7 and 6...h6. See also List of chess openings List of chess openings named after people References Further reading External links Petrov's Defence Video and explanation Petrov's defence (C42) – 365Chess.com ECO Games Gary Lane on the Cochrane Gambit Cochrane Gambit theory Chess openings