Tarrasch Defense

Instead of the traditional 3...Nf6, Black challenges d4 immediately with 3...c5, and after 4. cxd5 exd5 keeps a pawn on d5 rather than letting White dominate the center. The trade-off is structural. Once the c- and d-pawns are exchanged, Black is usually left with an isolated d-pawn, sometimes hanging pawns, in return for open lines and unobstructed development. The c8-bishop, the perennial problem piece of the Queen's Gambit Declined, has a clear diagonal. The c- and e-files are already half-open. White typically develops the knights and fianchettos the light-squared bishop to bear down on d5, aiming to blockade and eventually win the weak pawn.

5. Nf3, the Two Knights Variation, is the most popular reply, followed by the immediate 5. dxc5 and the quieter 5. e3. The Marshall Gambit, 5. e4, is a rare sideline. The engine judges the position as nearly level, and on Lichess decisive games are the norm, with White only slightly ahead in results. A related Pseudo-Tarrasch arises after 3. Nf3 c5.