4…Bb4This line of defence, called the McCutcheon variation, was recommended for many years by Tarrasch as being the strongest. The most obvious continuation 5 P—K 5 leads to complications, and the final verdict has not yet been reached. After 5...P—K R 3, the best continuation is thought to be: 6 P x Kt, P x B; 7 P x P, R—Kt 1; 8 P—K R 4, P x P; 9 Q—R 5, Q—B 3; 10 Q x R P, Q x P. White has an easy development, whilst Black, as in most variations in the French defence, finds it difficult to bring his Q B into play. After P—K R 3, it is not advisable to retire the Bishop; 6 B—R 4, P—K Kt 4; 7 B—Kt 3, for here the Bishop is out of play, and Black's King's Knight being free can play to K 5 for concerted action with Black's K B. Lasker's continuation in the present instance is at once simple and effective. It leads to an entirely different system of development.
5…Qxd5If Black recaptures with the pawn, he must lose a move with the Bishop in order to avoid getting an isolated doubled pawn after 6 Q—B 3. The doubled pawn which Black may get after the move in the text would not be isolated, and therefore not necessarily weak. It could become a weakness if Black were to castle on the King's side. But otherwise it might even become a source of strength, supporting, as it would, an advance of Black's K P against the White centre.
6…c5Black should retain the option of castling Q R, in case White exchanges at his K B 6; P—Q Kt 3 and B—Kt 2 would have been better.
12…Qb6Guarding against the mate at Q 1 before moving the Kt. But this would have been better effected by Q—K 2. After Q—Kt 3 the Knight cannot move yet because of B—Kt 5 ch.
17.Qe2Black wishes to push on the K P. White, however, prevents this at once.
18…Bb7The Black position has any number of weaknesses. The King cannot castle into safety; the pawn position is full of holes, and open to attack. White takes full advantage of this and wins in masterly fashion with a few strokes.
20…Rb8Now White cannot capture the Kt P because of B x Kt. But he does not want the pawn, he wants the King.
25.Qd6Mate in two was threatened (B—B 6 ch, etc.).
Edward Lasker, Chess Strategy (1921) · Public domain · source