Classical Variation, Noa Variation

With 4...d5 Black uses the time White spent on 4. Qc2 to stake a claim in the center immediately, fighting for e4 before castling. It is the third most frequent reply to the Classical Variation and, after the Berlin Variation (4...c5), one of its more combative options. The most common answer is 5. cxd5. After 5...exd5 6. Bg5 h6 7. Bh4 g5 8. Bg3 Ne4, Black has seriously loosened the kingside. In return Black gets active pieces, while White's c3-knight stays pinned and the bishop sits passively on g3. 5. Bg5 is also frequently played.

5. a3 Bxc3+ 6. Qxc3 is considered the more solid approach, since it forces the exchange of bishop for knight. The Main Line continues 6...Ne4, gaining time on the queen. Then 7. Qc2 Nc6 8. e3 e5 is the San Remo Variation. The Botvinnik Variation, 6...Nc6, develops the knight first. Castling with 6...O-O transposes to 4...O-O 5. a3 Bxc3+ 6. Qxc3 d5. After 7. Bg5 dxc4, the queen that recaptures on c4 can be harassed by ...b6 and ...Ba6. The engine rates the starting position as balanced, and White scores slightly better in online games.