Petrov's Defense

Petrov's Defense, also called the Russian Game or Petroff Defense, answers 2. Nf3 with 2...Nf6. Black leaves e5 unprotected and hits e4 instead. This sidesteps the Ruy Lopez, Italian Game and Scotch Game. The move appears in the Göttingen manuscript but was long neglected. It was revived in the 19th century through the analysis of the Russian masters Alexander Petrov and Carl Jaenisch, which is the source of both names.

The Classical Variation, 3. Nxe5, wins the pawn at once. Black cannot simply take back: the Damiano Variation, 3...Nxe4, runs into 4. Qe2, and 4...Nf6?? 5. Nc6+ wins the queen. Black therefore first plays 3...d6 to drive the knight back, and only after 4. Nf3 Nxe4 is the pawn regained. The Classical Attack, 5. d4, usually continues 5...d5 6. Bd3. This structure resembles an Exchange French with Black's knight posted on e4, and White tries to dislodge it with c4 and Re1. The Nimzowitsch Attack, 5. Nc3 Nxc3 6. dxc3, accepts doubled pawns for quick development, queenside castling and a kingside attack. The Cozio Attack, 5. Qe2, tends toward simplification after 5...Qe7 6. d3 Nf6. White can also deviate on move 4 with the Cochrane Gambit, 4. Nxf7, or the rarely effective Paulsen Attack, 4. Nc4.

The Modern Attack, 3. d4, was championed by Steinitz and has gained ground in the 21st century. Black usually replies 3...Nxe4, and after 4. Bd3 d5 5. Nxe5 the move 5...Nd7 is now the principal choice. Taking on d4 instead is less comfortable for Black: after 3...exd4 4. e5 Ne4 5. Qxd4 d5 6. exd6 Nxd6, Black's knight has been pushed around and White is slightly better.

Several third moves avoid the main theory. The Three Knights Game, 3. Nc3, is the most frequent choice in the online database. Black can transpose to the Four Knights with 3...Nc6, or keep the game independent with 3...Bb4. The Italian Variation, 3. Bc4, invites 3...Nxe4 4. Nc3, the Boden–Kieseritzky Gambit, while 3...Nc6 reaches a Two Knights Defense. On the Black side, the Stafford Gambit (3. Nxe5 Nc6 4. Nxc6 dxc6) is objectively dubious but full of traps. It became a common sight in online games after Eric Rosen promoted it.

The Petrov has a drawish reputation, although some lines are quite sharp. Elite players value it as a reliable defense, and world champions Smyslov, Petrosian, Karpov and Kramnik have all adopted it, as has Fabiano Caruana. Engines give White only a slight edge, and decisive results dominate in online play.