Petrov's Defence is a chess opening characterised by the following moves: 1. e4 e5 2. Nf3 Nf6
Although this counterattacking response to 2.Nf3 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 also called the Russian Game, which is the predominant name in some countries.
The Petrov has a drawish reputation, though there are attacking opportunities for both sides, and a few lines are quite . The Black counterattack in the also avoids the Ruy Lopez, Italian Game, and Scotch Game. White's most common response are 3.Nxe5 and 3.d4 (the Steinitz Variation).
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.
Main variations White's two main choices are 3.Nxe5 and 3.d4. 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".Janjgava (2001), p. 107
3.Nc3 may transpose to the Four Knights Game. 3.Bc4 may lead to the Boden–Kieseritzky Gambit or transpose to the Two Knights Defence or Bishop's Opening. Occasionally seen is the 3.d3.
Classical Variation: 3.Nxe5
After 3.Nxe5, the standard reply for Black is 3...d6 (3...Nxe4?! is usually considered an error). After 4.Nf3 Nxe4, White's main options are 5.d4, intending to undermine the knight on e4, and 5.Nc3, aiming for rapid development with queenside castling and a kingside attack. Other moves offer little hope for an advantage.
Main line: 3...d6 4.Nf3 Nxe4 5.d4 d5 6.Bd3 This is the most common line, reaching a position that has occurred in thousands of top-level games. The position is similar to an Exchange French in which Black has played the extra move ...Nf6–e4, though this extra move is not necessarily to Black's advantage. White will try to drive Black's advanced knight from e4 with moves like c4 and Re1. In practice White is usually able to achieve this, but at some structural cost such as having to play c4, which balances out.
A variety of sixth moves are possible for Black: 6...Bd6, 6...Be7, and 6...Nc6 are the most common. 6...Be7 and 6...Nc6 often transpose to the same line via 6...Be7 7.0-0 Nc6 or 6...Nc6 7.0-0 Be7. The most common move for White is then 8.c4.
Jaenisch Variation: 6...Be7 7.0-0 Nc6 8.c4
This line has been credited to Carl Jaenisch and has been popular for over a century. Black's most common reply to 8.c4 is 8...Nb4. After this, White usually retreats the bishop with 9.Be2, a line popularised by Anatoly Karpov. The main line of the variation continues 9...0-0 10.Nc3 Bf5 (or 10...Be6; 11.Ne5 is White's main reply) 11.a3 Nxc3 12.bxc3 Nc6 13.Re1 Re8. This line appeared twice in the Classical World Chess Championship 2004, where Vladimir Kramnik (playing White) was able to defeat Peter Leko in both games.
Most common for White after 13.Re1 Re8 is 14.cxd5 Qxd5, a position that can also be reached via 10.a3 Nc6 11.cxd5 Qxd5 12.Nc3 Nxc3 13.bxc3 Bf5 14.Re1 Re8, or via 13.cxd5 Qxd5 14.Re1 Re8 in the main line. If White delays the pawn capture, most often with 14.Bf4, Black may play 14...dxc4, continuing 15.Bxc4 Bd6, an important sideline. 13...dxc4 is also possible, but seems to leave White with an edge. Otherwise, after 14.cxd5 Qxd5, play tends to continue with 15.Bf4 Rac8, followed by 16.Bd3 or 16.h3.
After 9.Be2, other possible moves for Black are 9...dxc4 (which gives White an isolated queen's pawn), 9...Bf5, and 9...Be6. Queen exchanges via 10.Qa4+ Qd7 11.Qxd7+ can occur. 9...Be6 10.c5 is another notable line. On the ninth move, White may also allow Black to capture the bishop in exchange for the knight via 9.cxd5 or 9.Re1, but this is less well regarded than retreating.
Less common eighth-move alternatives for Black include: Retreating the knight with 8...Nf6. The line typically continues 9.Nc3 0-0 10.h3 Nb4 11.Be2 dxc4 12.Bxc4, and then most often 12...c6 13.Re1 Nbd5. There are also other move orders used to reach the same position. Aggressively developing the bishop with 8...Bg4. White's best move is 9.Nc3. The oldest reply, 8...Be6. It is considered playable but weak to 9.cxd5 Bxd5 10.Nc3 or 9.Re1 Nf6 10.c5.
8.Re1
8.Re1 is a serious (but less frequent) alternative to 8.c4. It was played by Emanuel Lasker at the Saint Petersburg 1895–96 chess tournament in a game against Harry Pillsbury. Though 8...Bf5 is also seen, the main reply for Black is 8...Bg4. Play may continue with 9.c4 Nf6, which tends to end up resulting in a reduction in central tension, or 9.c3 f5, a very sharp system.
After 9.c4 Nf6, play may continue with either 10.Nc3 Bxf3 11.Qxf3 Nxd4, 10.cxd5 Nxd5, or 10.cxd5 Bxf3 11.Qxf3 Qxd5, often leading to an endgame after 12.Qxd5 Nxd5. Both of the latter two continuations leave White with an isolated queen's pawn.
9.c3 f5 is a sharper continuation. The main line thereof is 10.Qb3 0-0 11.Nbd2 (11.Qxb7? is a trap) Na5, harassing White's queen. A even sharper and difficult to assess alternative is 11...Kh8, removing the Black king from a pin by White's queen on Black's d-pawn, preparing for 12...Rf6 and 13...Rg6, with the idea of attacking White's king, while allowing 12.Qxb7, which is now sound. 10...Qd6 is also possible for Black, though inferior to 10...0-0.
Marshall Variation: 6...Bd6 The main line of the Marshall Variation (6...Bd6) continues 7.0-0 0-0 8.c4 (8.Re1 is also possible). The most common move is then 8...c6, where White has the options of 9.Re1, 9.Nc3, 9.cxd5, and 9.Qc2, which was played against Howard Staunton in an 1851 game.
A common alternative to 8...c6 is 8...Bg4, played by Frank Marshall, the namesake of the variation. This line is also often reached via 7...Bg4 8.c4 0-0. Within this line, a famous trap is 9.cxd5 f5 10.Re1?! Bxh2+. After 11.Kxh2, Black can play 11.Nxf2, and White has nothing better than 12.Qe2 Nxd3 13.Qe6+ Kh8 14.Bg5, leaving Black up a pawn and with a safer king.
Other lines After 6...Be7 7.0-0 Nc6, 8.Nbd2 and 8.Nc3 are two modern tries for White that have emerged. After 6...Be7 7.0-0, 7...0-0 is an option for Black that avoids transposing to the frequently played 6...Nc6 lines. After 6...Nc6 7.0-0, 7...Bg4 is Black's only notable alternative to 7...Be7. 6...Bf5, typically combined with 7...Be7 (or in the move order 6...Be7 7.0-0 Bf5) is a lesser seen alternative line also tried by Karpov.
Nimzowitsch Attack: 5.Nc3
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 the doubled c-pawns will help protect the king, and that a strong 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.
Alternatives to 5.d4 and 5.Nc3 5.Qe2, the Lasker Variation, forces simplification and a likely draw after 5...Qe7 6.d3 Nf6. 5.d3 is a quieter line. Play may transpose into an Exchange French after 5...Nf6 6.d4 d5. 5.c4, the Kaufmann Attack, was also explored by Keres. The idea is to discourage ...d5 before undermining the Black knight on e4, however this plan is rather slow, and Black can instead choose to retreat the knight to g5, e.g. 5...Be7 6.d4 0-0 7.Bd3 Ng5 with equality. Alternatively, Black can counter White's plan with 5...Nc6, intending to answer 6.d4 with 6...d5!Janjgava (2001), pp. 131–33Yusupov (1999), pp. 42–59 5.Bd3 is the Millennium Attack.
Alternatives to 4.Nf3 4.Nxf7 (Cochrane Gambit). This line was labelled "speculative but entertaining" by Nick de Firmian in Modern Chess Openings.de Firmian (1999) He evaluates the position in Topalov–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. 4.Nc4 (Paulsen Variation). This move was labelled "ineffective" by de Firmian, though it is occasionally seen at grandmaster level. 4.Nd3 (Karklins–Martinovsky Variation). US master Andrew Karklins has experimented with 4.Nd3!?, now called the Karklins–Martinovsky Variation. Janjgava assesses it as "poor",Janjgava, p. 109 but it was played in the World Chess Championship 2018 between Magnus Carlsen and Fabiano Caruana.
Alternatives to 3...d6
Damiano Variation: 3...Nxe4
The Damiano Variation, 3...Nxe4, is usually regarded as an error, though it has occasionally been seen in recent grandmaster play. Black must play accurately to avoid an immediately losing position. After 4.Qe2 there are several moves that Black must avoid. 4...Nf6 5.Nc6+ wins the queen. 4...d5 5.d3 Qe7 6.dxe4 Qxe5 7.exd5 and Black loses a pawn. 4...d6? 5.Nxf7 Kxf7 6.Qxe4 and Black has lost a pawn and the ability to castle.
Best is 4...Qe7 5.Qxe4 d6 6.d4 dxe5 7.dxe5 Nc6, and after 8.Nc3 Qxe5 9.Qxe5+ Nxe5 10.Nb5 (or 10.Bf4) White has a moderate advantage.Janjgava (2001), pp. 108–09Yusupov (1999), pp. 12, 22–24
Stafford Gambit: 3...Nc6?!
Recently dubbed the Stafford Gambit, 3... Nc6 is considered dubious, but it sets a number of traps. It was advocated by Eric Rosen in the early 2020s and became popular in online games. After 4.Nxc6 dxc6, White wins a pawn but must play carefully. After 5.e5 (5.d3 is better) Ne4 6.d3?? (White should play 6.Nc3, 6.d4, or 6.Qe2) 6...Bc5! and White resigned in Lowens–Stafford, US correspondence game 1950.Forintos & Haág (1983), p. 110 Following 5.d3 Bc5, White must avoid the Légal Trap 6.Bg5?? Nxe4!, and if 7.Bxd8 (relatively best but still losing is 7.Be3) 7...Bxf2+ 8. Ke2 Bg4. Instead, White should play 6.Be2 h5 7.h3 (7.c3 with 8.d4 to follow is also good) and after 7...Qd6 8.c3 Black has insufficient compensation for the pawn, though White must still play carefully.Avetik Grigoryan, Stafford Gambit – The Refutation, Chessmood, 6 April, 2021
3...Qe7 3...Qe7 is inferior, as 4.d4 d6 5.Nf3 Qxe4+ 6.Be2 gives White a large lead in development.
Steinitz Variation: 3.d4
3.d4 was the preferred move of World Champion Wilhelm Steinitz, who recommended it in his The Modern Chess Instructor (1889) and played it three times against Harry Nelson Pillsbury in the Saint Petersburg 1895–96 tournament, winning two games and drawing one. It has become more popular in the 21st century, though still behind 3.Nxe5.
Black's most common reply is 3...Nxe4. After White's usual 4.Bd3, the main line continues 4...d5 5.Nxe5, followed 5...Nd7, a modern move that has become predominant, or the older symmetrical 5...Bd6.
The asymmetrical lines 4.dxe5 and 5.dxe5 are also not uncommon, particularly when White is determined to avoid a draw. 4.Nxe5 is also possible but uncommon as it gives Black the option to transpose to the Classical Variation with 4...d6. Otherwise, it usually reaches the 3.d4 Nxe4 4.Bd3 main line after 4...d5 5.Bd3.
Main line: 3...Nxe4 4.Bd3 d5 5.Nxe5 Nd7
After 3...Nxe4 4.Bd3 d5 5.Nxe5, Black's best regarded move is 5...Nd7, which has been advocated by Vladimir Kramnik, Viswanathan Anand, and others. White typically plays 6.Nxd7, 6.Nc3, or 6.0-0 in response. This line was considered problematic for Black until 1980, when Danish GM Bent Larsen played a pawn sacrifice in a game against World Champion Anatoly Karpov and won as Black. This brought great attention to 5...Nd7, which had not been Black's main reply at the time, as White was considered to have easy development after the sharp 6.Qe2.