Petrov's Defense: Three Knights Game: what to play after Nc3?

In Petrov's Defense: Three Knights Game (ECO C42), Black achieves the most reliable equality by playing Nc6. This natural developing move transposes into the Four Knights Game, neutralizing White's initiative and leading to an engine evaluation of -0.01. Across roughly 35 million recorded games in this position, Nc6 is by far the primary choice, appearing in 63.7% of encounters while holding White to a 52.5% scoring rate.

Transposition via Nc6

By developing the queen's knight with Nc6, Black defends the central pawn on e5 and symmetrically mirrors White's minor pieces. The continuation Nc6 d4 exd4 Nxd4 Bb4 Nxc6 illustrates central tension where Black challenges the white knight on d4 with active piece play. Opting for Nc6 avoids theoretical disadvantages and provides the soundest statistical foundation among Black's available options.

Active and Asymmetrical Alternatives

The primary alternative is Bb4, played in 17.1% of games (5.90M recorded), which leads to an evaluation of +0.32 while White scores 49.9%. Following Bb4 Nxe5 O-O Be2 Bxc3 dxc3, Black accepts a temporary pawn deficit to castle swiftly and damage White's queenside pawn structure. Another dynamic option is d5, seen in 5.3% of games with an evaluation of +0.69, where play can continue d5 exd5 Bd6 Bb5+ c6 dxc6.

Passive Options to Avoid

More passive setups concede greater central space to White without reciprocal activity. The solid d6 occurs in 13.0% of games with a +0.49 evaluation, after which the sample line d6 d4 Nbd7 h3 c6 g4 allows White expansion on both flanks. Worse is Bd6, chosen in only 1.0% of games (339K recorded) and yielding a +0.92 evaluation; the line Bd6 Nxe5 Bxe5 d4 Bd6 e5 grants White an advantageous central pawn fork.