Three Knights Game

The Three Knights Game, also known as the Three Knights Variation, is White's 3. Nc3 against Petrov's Defense. Instead of taking on e5 as in the Classical Variation or opening the center with 3. d4, White protects the e4-pawn with a developing move and leaves Black to decide what to do about the attacked e5-pawn. White often chooses it to sidestep the lines that belong to the Petrov alone. The same position can arise from the Vienna Game after 1. e4 e5 2. Nc3 Nf6 3. Nf3. In the online database it is the most frequent third move for White against the Petrov, and its position is among the more commonly reached of all named openings.

Because e5 is still en prise, Black's most natural answer is 3...Nc6, which accounts for almost half of all games and is considered the best-regarded reply. It defends the pawn and transposes directly to the Four Knights Game. For a Petrov player this means exchanging the familiar symmetrical structures of the Russian Game for Four Knights theory, which is the price of meeting White's move with the simplest developing reply.

The main way to keep the game independent is 3...Bb4. Black does not defend e5 and instead pins the c3-knight, so that White's e4-pawn loses its defender if the knight on f3 takes on e5. After 4. Nxe5 O-O 5. Be2 Re8 6. Nd3 Bxc3 7. dxc3 Nxe4 8. Nf4 d6 9. O-O, Black has recovered the pawn, but White holds a slight advantage thanks to the bishop pair and the open lines for both bishops, while the doubled c-pawns are of little consequence. In the database the results after 3...Bb4 are almost exactly even.

The bishop sortie 3...Bc5 is the second most popular move in online play, though it also leaves e5 unprotected and does not feature in the standard treatments of the line. Engines rate the position as roughly balanced and list 3...Nc6, 3...Bb4 and 3...d6 as Black's soundest options. Online games from this position seldom end in draws, and White scores slightly better than Black overall.