Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. c3/3...Nf6/4. d4/4...Nxe4

4...Nxe4 takes White's undefended e4 pawn. This move is the main continuation at higher levels.^[1] Black's knight on e4 also pressures White's f2 pawn, which will become a serious threat if Black can get their bishop to c5. How White recovers their pawn with or without allowing ...Bc5 determines how the game proceeds.

If White thinks they are simply trading pawns, because they have two attackers on e5 to Black's one defender, they are mistaken. As soon as White gives up control of c5, after 5. dxe5? or 5. Nxe5? Nxe5 6. dxe5, Black has ...Bc5!. Black's knight and bishop co-ordinate against f2, threatening to pick up a pawn and either fork the queen and rook or force White to lose castling rights. Black also threatens ...Qh4.

The intermezzo 5. d5 is the mainline and traditional Ponziani move. White's idea is to first kick the knight, and after it moves to recover the pawn safely without the threat of Bc5.

After 5...Ne7 (mainline), now White can capture the pawn 6. Nxe5 because Bc5 is not legal. After 6. Nxe5, Black's knight reroutes to g6: 6...Ng6 7. Nxg6 hxg6 Black gets the open h-file, and after 8. Qe2 Black is no longer in time for ...Bc5. If Black tries 5...Nb8 then 6. Nxe5 Bc5 is possible, but White can answer it with Nd3 to defend f2. (If 5...Na5? 6. c4 traps the knight.)

However, 5. d5 also gives up control of c5 and so Black can choose to play 5...Bc5 immediately. This cunning knight sacrifice is the sharp Vukovic gambit, which brings Black the most practical success in the position.

The engine line is actually 5. Bd3. By keeping the pawn on d4, White prevents any complications involving ...Bc5. After 5...d5 defending the knight (5...Nf6?! gives up pressure on f2 and 6. dxe5 recovers the pawn with tempo) 6. Nxe5= White recovers the pawn and the game is even.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3 Nc6 3. c3 Nf6 4. d4 Nxe4

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Wikipedia has related information at Ponziani opening