Advance Variation, Botvinnik-Carls Defense

The Botvinnik-Carls Defense answers the Advance Variation with 3...c5, hitting d4, the base of White's pawn chain, before developing the queen's bishop. It is the second most frequent reply to 3. e5, behind 3...Bf5. The c-pawn needs two moves to reach c5, but Black gains immediate central friction and keeps the c8-bishop unobstructed for the moment. White has to decide whether to support d4, trade on c5, or let Black exchange and recapture with a piece.

In practice 4. c3, which prepares to meet ...cxd4 with cxd4, is chosen in roughly half of all games. Theory treats it as a minor sideline, but it is very popular at amateur level. Black is under no obligation to capture on d4 straight away and can keep the tension while completing development. Black scores slightly better than White after this move in the database.

The engine prefers 4. Nf3 and 4. dxc5, and 4. dxc5 gives White the best results of the main replies. Taking on c5 removes the e5-pawn's support, and Black usually aims to regain the c-pawn without hurry rather than chase it. A typical sequence is 4...Nc6 5. f4 e6 6. Be3 d4 7. Bf2 Bxc5, in which material is level again but White keeps a small edge, partly because ...e6 has shut in Black's light-squared bishop. After 4. Nf3 cxd4 5. Nxd4 Nc6, the e5-pawn again lacks protection, and White can reply 6. Nxc6 bxc6 7. Bd3. Black's structure turns into a c6-d5 pawn pair with a half-open b-file, while the bishop on d3 controls f5 and stops Black's queen's bishop from reaching an active square.

The line is named after Carl Carls, who played it at Breslau in 1912, and Mikhail Botvinnik. It stayed uncommon until Botvinnik used it in his 1961 return match against Mikhail Tal. Botvinnik won the match and regained the world title, but this variation brought him only two draws and a loss. Across the database Black scores marginally more wins than White after 3...c5, and the engine assessment is close to equality.