Chess Opening Theory/1. e4/1...Nf6/2. e5/2...Nd5/3. d4

Alekhine's defence
	a b c d e f g h 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 a b c d e f g h
	Position in Forsyth-Edwards Notation (FEN) rnbqkb1r/pppppppp/8/3nP3/3P4/8/PPP2PPP/RNBQKBNR
	Moves: 1. e4 Nf6 2. e5 Nd5 3. d4
	ECO code: B02
	Parent: Alekhine's defence

3. d4

Black's knight is safe for now, which gives them the opportunity to start the counterattack on White's advanced pawns.

3...d6 is the main move. This threatens ...dxe5 and opens a line for Black's bishop to develop. This is the best direction to develop the bishop in because Black anticipates that White may kick their knight again soon, and they certainly don't want to play ...b6 & ...Bg7 and take away the knight's retreating square. The main responses are 4. c4 Nb6 5. f4, the four pawns attack, where White intends to recapture on e5 with the f-pawn, and 4. Nc3, intending to recapture on e5 with the knight.

3...b5?! is the dubious but tricky O'Sullivan gambit. After White takes the free pawn, 4. Bxb5, the idea is 4...c5, a tempo move to open the queen where 5. dxc5?? loses to 5...Qa5+ 6. c3 Qxb5 winning the bishop, and 7. Qxd5?? to take the "hanging" knight runs afoul of 7...Bb7!, skewering the queen to g2 and the undefended rook.

Attacking the base of White's pawn chain, 3...c5?, is not ideal because 4. dxc5 takes away the b6 square while discovering an attack on the knight.

Theory table

1. e4 Nf6 2. e5 Nd5 3. d4

	3	4	5	6	7	8
Modern variation	... d6	Nf3 Bg4	Be2 e6	O-O Be7	c4 Nb6	Nc3 O-O	⩲/±
Exchange variation	... ...	c4 Nb6	exd6 cxd6	Nf3 g6
Four pawns attack	... ...	... ...	f4 dxe5	fxe5 Nc6	Be3 Bf5
O'Sullivan gambit	... b5?	Bxb5 c5					∓