Chess Opening Theory/1. e4/1...c5/2. d4/2...cxd4

Black takes the pawn. The trade of a c- for d-pawn gives Black a central pawn majority.

Though White could take it back with 3. Qxd4?!, this allows Black to push the queen around and play 3...Nc6 with tempo.

Instead the main move is to gambit the pawn, offered by 3. c3. After 3...dxc3 White can retake while developing their knight.

An alternative is 3. Nf3, the Morphy gambit. White prepares to recapture with the knight: if Black tries to hold onto the extra pawn 3...e5 4. c3 is a "good" version of the Smith-Morra, where Black has a hole on d5 and a backward d-pawn. Instead this can transpose into an Open Sicilian after (e.g.) 3...d6 4. Nxd4.

2. d4 was in vogue in the mid-18th century. Jaenisch, in his 1842 book of analysis, gave 2. d4 as White's best move against the Sicilian. 3. Qxd4 and 3. Nf3 were the continuations of the day; Jaenisch's gave preference to 2...cxd4 3. Qxd4, even though 3...Nc6 4. Qd1 allows Black to gain time on the queen.^[1]:25-28

An early appearance of the gambit 3. c3 was in 1846 in Kieseritzky v Vitzthum.^[2] It went largely un-played for the next century, aside from a few games in the 1920s and 1930s, until it was revived in the 1950s. Kenneth Smith (1930―1999) and Pierre Morra (1900―1969) independently published analysis of it in the 50s. Another proponent was Milan Matulović (1935―2013), after whom it was sometimes called (the Matulović gambit).

Its leading proponent today is Marc Esserman (1983―).

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1. e4 c5 2. d4 cxd4

Wikipedia has related information at Smith-Morra Gambit.

• Smith-Morra - Chessgames.com