Winawer Variation, Advance Variation

With 4. e5 White closes the center and adopts an Advance-style pawn chain while the bishop on b4 still pins the knight. This is the main line of the Winawer, classified as ECO C16. Because the knight already occupies c3, the usual Advance support with c2-c3 is unavailable, so the d4 base is harder to maintain. Black exploits this chiefly with 4...c5, by far the most common reply, which also takes away the bishop's retreat and usually prompts 5. a3 Bxc3+ 6. bxc3. White can instead play the Moscow Variation, 5. Qg4, hitting g7 at once. After 5. a3 Bxc3+ 6. bxc3 Ne7, branches include 7. h4, gaining kingside space, and 7. Bd3.

Black's other options alter the move order. 4...Ne7 keeps ...c5 in reserve; after 5. a3 Bxc3+ 6. bxc3 c5 the Smyslov Variation continues 7. a4. 4...Qd7 is the Petrosian Variation, which has scored well for Black in online play, whereas the immediate 4...Bxc3+ gives White noticeably better results. The engine rates the position as a slight edge for White, while practical results overall are close to even.