Petrov's Defense: what should White play?

In Petrov's Defense (ECO C42), the critical position arises after Black attacks the e5 with d6. The primary and theoretically sound recommendation for White is Nf3, which safely preserves the piece, controls central squares, and holds an engine evaluation of +0.29.

The main line with Nf3

The retreat Nf3 represents the overwhelming consensus among practitioners, appearing in 84.8% of recorded games (7.91M recorded) where White scores 52.8%. Retreating the knight to f3 avoids material loss and prepares harmonious piece development and central expansion. An illustrative continuation demonstrating standard central play is Nf3 Nxe4 d4 d5 Bd3 Bf5, where White establishes a solid central foothold.

Alternatives on move four

White occasionally explores other knight retreats. The move Nc4 has been chosen in 4.4% of games (406K recorded), scoring 48.7% with an engine evaluation of -0.01; an illustrative engine line runs Nc4 Nxe4 Qe2 Qe7 Ne3 Be6. Another quiet option is Nd3, tried in 2.6% of games (245K recorded) with an evaluation of +0.02 and a 49.6% score for White, typically leading into Nd3 Nxe4 Qe2 Qe7 Nf4 Nc6.

Dubious tries and sacrifices

A combative option is Nxf7, played in 7.8% of games (729K recorded). Although it scores 52.4% for White across all levels, the engine rates it at -1.12, favoring Black in the continuation Nxf7 Kxf7 Nc3 Be6 d4 Kg8. Finally, Bb5+ drops significant material and clarity, evaluated at -2.64; it appears in only 0.4% of games (38K recorded) and scores just 39.1% following Bb5+ c6 Nxf7 Kxf7 Bd3 Nbd7.