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Petrov's Defence (sometimes spelled Petroff's) is the chess opening

1.e4 e5

2.Nf3 Nf6

Though this symmetrical response has a long history, it was first popularized by Alexander Petrov � a Russian chess player of the mid-19th century. In recognition of the early investigations by the Russian masters Petrov and Carl Jaenisch, this opening is called the Russian Game in some countries. The Petrov has a reputation of being dull and uninspired. However, it offers attacking opportunities for both sides, and many lines are quite sharp. Pillsbury's game in 1896 against Emmanuel Lasker testifies to this. The Black counterattack in the center also avoids the Ruy Lopez and Giuoco Piano.

If White defends his attacked king pawn with 3. Nc3, Black can obtain equal chances by transposing into the Four Knights Game with 3...Nc6 or by entering the Petrov's Three Knights Game with 3...Bb4.

Another possibility is 3.Bc4 Nxe4 4.Nc3, the Boden-Kieseritzky Gambit. It is not considered dangerous, since Black has several viable options. He can accept the gambit with 4...Nxc3 5.dxc3 f6, although he must play carefully after 6.0-0 (for example 6...Be7?? 7.Qd5! and 6...Bc5?? 7.Nxe5! are disastrous; 6...d6 and 6...Nc6 are playable). Another possibility is returning the gambit pawn with 4...Nxc3 5.dxc3 c6 6.Nxe5 d5, which equalizes. A third possibility is transposing to the Italian Four Knights Game with 4...Nc6, and if 5.Nxe4, d5. If 5.Bxf7+?, Kxf7 6.Nxe4 d5 gives Black the bishop pair and control of the center. If 5.0-0, Black plays 5...Nxc3 6.dxc3 and now Black can play 6...Qe7 7.Ng5 Nd8, as recommended by Fischer in My 60 Memorable Games, or 6...f6 transposing to the main line of the Boden-Kieseritzky.

White usually prefers 3.Nxe5, the Classical Variation, or 3.d4, the Steinitz Variation.

After 3.Nxe5, Black should not continue to copy White's moves and try to restore the material balance immediately with 3...Nxe4? because after 4. Qe2 White will either win material (4...Nf6?? 5.Nc6+ wins Black's queen, and after 4...d5 5.d3 Qe7 6.dxe4 Qxe5 7.exd5 Black loses a pawn), or obtain a superior position (4...Qe7 5.Qxe4 d6 6.d4 f6 7.Nc3 dxe5 8.Nd5 Qd6 9.Bf4 Nd7 10.0-0-0 and White has a big advantage). Black usually plays 3...d6. White can make a speculative sacrifice by trying the Cochrane Gambit with 4.Nxf7?!. More often, White follows the main line 4.Nf3 Nxe4 5.d4 d5 6.Bd3, where he will try to drive Black's advanced knight from e4 with moves like c4 and Re1. White can instead force simplification with Lasker's 5.Qe2 Qe7 6.d3. This is generally only good enough for a draw, but Black must avoid this line if he is playing for a win. Another possibility, explored by Keres, is 5.c4.

Steinitz favored 3.d4. Black can capture either white pawn. After 3...exd4 4.e5 (4.Bc4 transposes into the Bishop's Opening) Ne4 5.Qxd4 d5 6.exd6 Nxd6 7.Nc3 Nc6 8.Qf4 the game is approximately equal. After the other capture, 3...Nxe4, 4.Bd3 d5 (amazingly, 4...Nc6!? 5.Bxe4 d5, intending 6.Bd3 e4, is also possible) 5.Nxe5, either 5...Nd7 or 5...Bd6 gives roughly equal chances.

Karpov, Yusupov, Marshall, and Pillsbury have frequently played the Petrov as Black.

The ECO codes for Petrov's Defence are C42 (for White moves other than 3.d4) and C43 (for 3.d4).

Here are two a games illustrating the attacking possibilities open to both sides:

Browne-Bisguier, U.S. Championship 1974 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Be7 7.O-O Nc6 8.c4 Nb4 9.cxd5 Nxd3 10.Qxd3 Qxd5 11.Re1 Bf5 12.Nc3 Nxc3 13.Qxc3 c6? (13...Be6! gives Black good chances to equalize after 14.Qxc7 Bd6 followed by 0-0, or 14.Re5 Qc6) 14.Bh6!! Rg8 (14...gxh6 15.Re5! Qd7 16.Rae1 Be6 17.d5! cxd5 18.Rxe6 fxe6 19.Qxh8+ wins) 15.Re5 Qd7 16.Rae1 Be6 17.Ng5 O-O-O 18.Nxf7 Bxf7 19.Rxe7 Qxd4 20.Rxf7 Qxc3 21.bxc3 gxh6 22.Rb1 Rg5 23.h4 Rb5 24.Rxb5 cxb5 25.Rxh7 Rd1+ 26.Kh2 Rd2 27.Rxh6 Rxa2 28.h5 Rxf2 29.Rh8+ Kc7 30.h6 Kb6 31.Kh3 a5 32.g4 b4 33.cxb4 axb4 34.Re8 Rf1 35.Kg2 Rf7 36.g5 Rf5 37.h7 Rxg5+ 38.Kf3 Rh5 39.h8=Q Rxh8 40.Rxh8 1-0

Ljubojevic-Makarychev, Amsterdam 1985 1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 Nc6 7.O-O Be7 8.Re1 Bg4 9.c3 f5 10.Qb3 O-O 11.Nfd2? Nxf2! 12.Kxf2 Bh4+ 13.g3 f4! 14.Kg2 fxg3 15.Be4 Bh3+ 16.Kg1 gxh2+ 17.Kxh2 Qd6+ 18.Kh1 Bxe1 19.Qxd5+ Qxd5 20.Bxd5+ Kh8 21.Nf3 Bg3 22.Ng1 Bf1 23.Nd2 Rae8 24.Ne4 Rxe4 25.Bxe4 Rf2 26.Nf3 Bg2+ 27.Kg1 Bxf3 28.Bxf3 Rxf3 0-1