Classical Variation, Zukertort Gambit

The Zukertort Gambit arises from the Berlin move order 3...Nf6 4. O-O Bc5, or from the Classical Variation by transposition. With 5. c3 White prepares d4 to gain time against the bishop on c5 and leaves e4 unprotected. Accepting with 5...Nxe4 adds pressure on f2, and careless play is punished. 6. Re1 is a blunder because of 6...Bxf2+ or 6...Nxf2. Blocking the bishop with 6. d4 is possible, but 6. Qe2 is considered best. It attacks the knight, and White eventually regains the pawn, often with more.

Black more often declines with 5...O-O, also the engine's preference. Then 6. d4 builds a broad center with gain of tempo, and 6...Bb6 7. Bg5 is the Modern Main Line. The second most common reply, 5...d6, scores poorly for Black in practice. 5...a6 is regarded as a mistake. After 6. Bxc6 dxc6, the ...Qd4 resource familiar from Exchange Variation structures is ruled out by the pawn on c3. Engines give White a slight edge, and White scores well in online games.