Chess Openings Lab
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Petrov's Defense: Three Knights Game

The Three Knights Game in the Petrov is 3.Nc3, where White defends e4 with a knight instead of taking on e5. White keeps the game quiet and flexible, while Black can transpose to the Four Knights with 3...Nc6 or play independently with 3...Bb4.

Moves
1.e4 e5 2.Nf3 Nf6 3.Nc3
ECO
C42
Engine
+0.10 · level (Stockfish 17.1, depth 20)
Played
15,724 games in our lichess sample
White scores
52.3%

Key ideas for both sides

White

  • Against 3...Nc6, play 4.d4 exd4 5.Nxd4 for an open Scotch-style Four Knights.
  • After 3...Bb4 take on e5 with 4.Nxe5, then use Nd3 to hit the bishop and keep the extra pawn for a while.
  • Against 3...d6, gain space with d4, h3 and even g4 to attack Black's quiet setup.
  • Use Bd3 and O-O after ...Bb4 and ...Nxc6 trades to finish development.

Black

  • 3...Nc6 leads to the Four Knights; after 4.d4 exd4 5.Nxd4 Bb4 the pin on c3 gives Black play.
  • 3...Bb4 4.Nxe5 O-O lets Black regain the pawn on e4 after ...Bxc3 and ...Nxe4.
  • Keep e5 solid with ...d6 and ...Nbd7 for a Philidor-like setup, but expect a kingside pawn storm.
  • Pin and trade on c3 to double White's pawns when it gains time.

Plans and pawn structure

After 3...Nc6 4.d4 exd4 5.Nxd4 Bb4, Black pins c3 and often gives White doubled c-pawns, then plays ...O-O, ...Re8 and ...d5. White aims for Bd3, O-O and Bg5, using the bishop pair. In the 3...Bb4 line, material comes back on e4 and the game opens with chances for both. The 3...d6 setup is more closed, and White plays for space on the kingside with h3 and g4.

What the engine plays from here

Stockfish 17.1 at depth 20 rates the position +0.10: level. Its three top choices for Black:

  1. +0.10 3...Nc6 4.d4 exd4 5.Nxd4 Bb4 6.Nxc6
  2. +0.35 3...Bb4 4.Nxe5 O-O 5.Nd3 Bxc3 6.dxc3
  3. +0.51 3...d6 4.d4 Nbd7 5.h3 c6 6.a4

Pawns, from White's side.

How it scores on lichess

15,724 rated lichess games reached this position; White scored 52.3%.

under 120054.5%
1200–159951.4%
1600–199951.6%
2000 and up52.2%

Light: White wins. Grey: draws. Dark: Black wins. About the sample.

Where it goes next

  • Spanish Variation, Symmetrical Variation, Tarrasch Variation3...Nc6 · rare

How to play against it

As Black, the simplest answer is 3...Nc6, reaching a sound Four Knights. If you want to keep Petrov character, try 3...Bb4 and win back e4 with ...Bxc3 and ...Nxe4. Avoid passive setups unless you are ready for White's kingside expansion.

Questions

What are the moves of the Petrov's Defense: Three Knights Game?

The Petrov's Defense: Three Knights Game starts 1.e4 e5 2.Nf3 Nf6 3.Nc3. Its ECO code is C42.

Is the Petrov's Defense: Three Knights Game good for White?

Stockfish 17.1 rates the position +0.10 at depth 20, which is level. In 15,724 lichess games from our sample, White scored 52.3%. A flexible choice for White players who want to avoid Petrov theory, while Black needs to know the Four Knights or the ...Bb4 setup.

What is the main idea of the Petrov's Defense: Three Knights Game?

White defends e4 with a knight and steers toward Four Knights positions. Black can transpose with 3...Nc6 or play 3...Bb4, pinning c3 and planning to win back e4.

What should Black play next?

The engine's first choice is Nc6, with Bb4 and d6 close behind. 3...Nc6 transposes to the Four Knights, where Black gets easy development and a solid position.

Updated October 2026. Sources and method.