Petrov's Defence or the Petrov Defence (also called Petroff Defence, Petrov's Game, Russian Defence, or Russian Game – ) is a chess opening characterised by the following moves: 1. e4 e5 2. Nf3 Nf6
Though this response has a long history, it was first popularised by Alexander Petrov, a Russian chess player in 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 drawish reputation; however, it offers attacking opportunities for both sides, and a few lines are quite . Often a trade occurs and Black, after gaining a tempo, has a well-placed knight. Pillsbury's game in 1895 against Emanuel Lasker testifies to this. The Black counterattack in the also avoids the Ruy Lopez, Giuoco Piano (and other lines of the Italian Game), and the Scotch Game. The Petrov has been adopted by many of the world's leading players, including world champions Vasily Smyslov, Tigran Petrosian, Anatoly Karpov, and Vladimir Kramnik, along with grandmaster Fabiano Caruana and others.
The Encyclopaedia of Chess Openings codes for Petrov's Defence are C43 (for 3.d4) and C42 (for all other lines).
White's third move
White's two main choices for move three are 3.Nxe5, the Classical Variation and 3.d4, the Steinitz Variation. 3.Nxe5 is more popular but they often lead to similar positions and "there is no clear reason to prefer one move over the other".
3.Nc3 may transpose to the Four Knights Game or the Three Knights Game. 3.Bc4 may lead to the Boden–Kieseritzky Gambit or transpose to the Two Knights Defence. Occasionally seen is the 3.d3.
Classical Variation: 3.Nxe5
After 3.Nxe5, the Classical Variation, by far the most popular move for Black is 3...d6. Black should not continue to copy White's moves with 3...Nxe4. After 4.Qe2 Black cannot play 4...Nf6 because 5.Nc6+ wins the queen, and after 4...d5?! 5.d3 Qe7 6.dxe4 Qxe5 7.exd5 Black loses a pawn. Relatively best for Black is 4...Qe7 5.Qxe4 d6 6.d4 dxe5 7.dxe5 Nc6, and after for example 8.Nc3 (8.Bb5 is also good) 8...Qxe5 9.Qxe5+ Nxe5 10.Nb5 (or 10.Bf4) White has a clear advantage. Also inferior for Black is 3...Qe7?! when 4.d4 d6 5.Nf3 Qxe4+ 6.Be2 gives White a large lead in development.
Most often, White follows the main line 3...d6 4.Nf3 Nxe4 5.d4 (5.Bd3 is also playable, known as the Millennium Attack) d5 6.Bd3, where he will try to drive Black's advanced knight from e4 with moves like c4 and Re1. If White achieves this, then he is up two tempi (Nf6–e4–f6, plus the tempo White starts the game with). In practice White is usually able to achieve this, but at some structural cost such as having to play c4, which balances out. White can also force simplification with Lasker's 5.Qe2 Qe7 6.d3. This is generally only good enough for a draw, which Black should be satisfied with. Another possibility, explored by Keres, is 5.c4, known as the Kauffmann Attack.
A completely different approach is to meet 4...Nxe4 with 5.Nc3 Nxc3 6.dxc3 with rapid and castling. For instance, White can plan a quick Be3, Qd2, and 0-0-0, and play for a attack, trusting that his doubled c-pawns will help protect his king, and that his initiative and attacking potential will offset the longterm disadvantage of having doubled pawns. In the 5.Nc3 line, Black must avoid 5...Bf5?? 6.Qe2! which wins a piece due to the pin (if 6...Qe7 7.Nd5, forcing 7...Qd7 because of the threat to the c7-pawn; then 8.d3 wins the piece). Viswanathan Anand resigned after only six moves after falling for this against Alonso Zapata at Biel in 1988.
The Cochrane Gambit, 4.Nxf7, is labelled "speculative but entertaining" by Nick de Firmian in Modern Chess Openings (MCO) 14th edition. He evaluates the position in Veselin Topalov–Vladimir Kramnik, Linares 1999 as offering chances for both sides after 4...Kxf7 5.Nc3 c5!? 6.Bc4+ Be6 7.Bxe6+ Kxe6 8.d4 Kf7 9.dxc5 Nc6.
The Paulsen Variation, 4.Nc4, is labelled "ineffective" by de Firmian in MCO, but is occasionally seen at grandmaster level. US master Andrew Karklins has experimented with 4.Nd3!?, now called the Karklins–Martinovsky Variation. This was played in the World Chess Championship 2018 between Magnus Carlsen and Fabiano Caruana.