Philidor Countergambit, Zukertort Variation

The Zukertort Variation meets the Philidor Countergambit with 4. Nc3, which protects e4 with a developing move and leaves the central tension for Black to resolve. Engines give White a clear advantage, and White scores better than Black in practice. Black usually takes with 4...fxe4, and 5. Nxe4 d5 is the trap: 6. Nxe5 dxe4 7. Qh5+ g6 8. Nxg6 leaves Black in serious trouble, since 8...hxg6 9. Qxh8 costs the rook. Against 5...d5, the strongest line is 6. Neg5 exd4 7. Bb5+ c6 8. O-O, when White is close to winning. Black does better with 5...Nf6 6. Nxf6 gxf6 7. dxe5 dxe5, which accepts a broken kingside but gives realistic chances of holding the balance.

The second most common reply, 4...exd4, gives up the center, and 5. Nxd4 fxe4 6. Bc4 Nf6 7. O-O gives White a large lead in development. The advance 4...f4 is the least successful of the common replies, and Black scores poorly with it. Engines also consider the quieter 4...Be7 and 4...Nc6.