Petrov's Defense

The Petrov's Defense, also called the Russian Game is a King's Knight opening classified as C42-43 in the ECO code, named after Russian master Alexander Petrov. The opening moves are:

1. e4 e5
2. Nf3 Nf6

It is one of three soundly regarded responses by black to 2. Nf3, the King's Knight Opening.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

The Petrov's Defense.

Classical Variation

In the classical variation, white captures black's pawn with 3.Nxe5. Black has a number of choices to play here.

Damiano Variation

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

The Damiano Variation in the Classical Variation.

If black responds with 3...Nxe4, this is the Damiano Variation. Immediately recapturing may seem the most obvious response, however it allows white a significant advantage because of 4.Qe2.

Black's moves in this position are:

• Moving the knight away, where 5.Nc6+ wins a Queen.
• Protecting Black's knight, just attack it with 5.d3.
• Attacking White's knight, take Black's free knight with 5.Qxe4 and if the opponent takes the knight, then go 6.Qxe5+.
• If any random move, then take the free knight with 5.Qxe4.

The best moves for both players are:

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

The Petrov's Defense.

Classical Variation

3... Nxe4
4. Qe2 Qe7
5. Qxe4 d6
6. d4 dxe5
7. dxe5 Nc6
8. Nc3 Nxe5
9. Qxe5 Qxe5+
10. Nxe5

All of black's moves after 3...Nxe4 are forced by threat of losing material.

A better move for black is the Stafford Gambit, 3...Nc6. This leads to 4. Nxc6 dxc6, and white is up a pawn, but black has the option of a number of dangerous traps. However, if white evades these traps, they will have a significant advantage.

Generally, it is widely accepted that the best move for black is 3...d6, which kicks White's knight away and allows the bishop to develop. White has four plausible continuations below.

4.Nf3: Main Line

Black should respond with Nxe4, recapturing the pawn. The most common line is 5. d4 d5 6. Bd3, with white attempting to kick black's knight. If successful, white is up a free tempo, giving them an advantage.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3,

the Petrov's Defence, Classical, Main Line

The other common line is 5. Nc3 Nxc3 6. dxc3, which allows white a strong queenside castle after developing the queen and bishop. However, the doubled pawns will likely turn against white as a disadvantage in the endgame. This second line also holds a trap if black plays 5... Bf5, as white can play Qe2. THis leads to 6... Qe7 7. Nd5 (threatening the queen, as well as a fork of the king and rook), then black must play Qd7; 8. d3 wins the knight.

4. Nd3, the Karklins-Martinovsky Variation

Considered a weak move for white, Magnus Carlsen played it against Fabiano Caruana in 2018 (they tied). The continuation in that game was

4... Nxe4
5. Nc3 Nf6
6. Nf4 c6
7. d4 d5

and the game is equal.

4. Nc4, the Paulsen Variation

This variation is named after German master Louis Paulsen. It is very rarely seen, and provides interesting positions for both players. Black should respond with Nxe4, equalising material; 5. Nc3 Nxc3 6. dxc3 (or bxc3) and white has a clear developmental advantage.

4. Nxf7, the Cochrane Gambit

The Cochrane Gambit, named after scottish master John Cochrane, sees white gambit their knight to disrupt black's defenses. Black must recapture with king, but this will lead to a weakened king position in the middle game. An example of a continuation is below, as played by Topalov-Kramnik in 1999.

4. Nxf7 Kxf7
5. Nc3 c5
6. Bc4+ Be6
7. Bxe6+ Kxe6
8. d4 Kf7
9. dxc5 Nc6

but according to Stockfish, you should play 5... Be6 instead of 5.. c5

3. d4, the Steinitz Attack

The second most common response by white to Petrov's Defense is the Steinitz (Modern) Attack. This variation is classified as ECO C43; all other moves by white are C42. Read that article for the theory.

Other Options for White

There are two other interesting, if not highly regarded, continuations for white's third turn.

3. Nc3 is Petrov's Three Knights Game. The main line here for black is Bb4, but more often black will respond with Nc6, transposing to the Four Knights Game.

3. Bc4 is the Boden-Kieseritzky Gambit. This gambits white's king pawn to Nxe4; however, black may also decline the gambit and respond with 3... Nc6, transposing to the Two Knights Defense of the Italian Game.

Sources

• Wikipedia
• Kenilworth Chess Club
• Chess.com - Carlsen vs Caruano