Sicilian Defense, O'Kelly Variation

The O'Kelly Variation begins 1.e4 c5 2.Nf3 a6. The move ...a6 prevents Bb5+, a bishop check that can exchange a piece or alter Black's pawn arrangement in other Sicilians. It also prepares ...b5, which can control more squares on the queen's side.

The idea has a cost: ...a6 does not move a piece from its starting square or directly contest the central squares. White is therefore not required to enter an Open Sicilian, the name for lines in which White plays d4 and Black exchanges the c-pawn for that central pawn. White can play c3 to prepare d4 with extra support, c4 to control d5, or another setup intended to exploit the move Black spent on ...a6.

After 3.d4 cxd4 4.Nxd4, Black can answer ...e5. The d4-knight must move, and b5 is controlled by the a6-pawn, which explains the precise sequence. This is a move-order opening: the value of ...a6 depends on the options it removes and the alternatives it gives White.

It should not be confused with an early Najdorf. The Najdorf arises after more pieces have moved and includes ...d6 and ...Nf6. Nor is every white b4 advance the same gambit: the Wing Gambit starts immediately with 2.b4.