Berlin Defense, Improved Steinitz Defense

The Improved Steinitz Defense arises when Black answers 4. O-O in the Berlin Defense of the Ruy Lopez (Spanish Game) with 4...d6 rather than 4...Nxe4 or 4...Bc5. Black declines the simplifying route toward the Berlin endgame and instead props up e5 with a pawn, adopting the structure of the old Steinitz Defense, 3...d6, but with the king's knight already developed. The two lines can transpose. The usual cost of this setup applies: the f8-bishop is hemmed in behind d6 and generally goes to e7, and Black holds the e5 point rather than contesting the center directly.

With e5 now protected, ...Nxe4 becomes a genuine threat to win a pawn. White's two most frequent replies deal with it in different ways. 5. Re1, by far the most common, covers e4 from the e-file, while 5. d3 defends it with a pawn. 5. d4, the engine's top choice, instead challenges Black's center at once. White scores well after 5. Re1 and 5. d4, whereas 5. d3 yields roughly even results. The engine gives White a slight edge.