Petrosian Variation

The Petrosian Variation, also called the Petrosian System, spends a tempo on 4. a3 to take the b4-square away from Black's king's bishop. With the pin on a knight at c3 ruled out, White can develop that knight and aim for e2-e4 and a broad pawn center. Black's usual answer is 4...Bb7, by far the most popular move, which keeps watch over e4 and is often backed up by ...d5 to contest the square directly. Garry Kasparov played the line regularly early in his career.

The quiet pawn move leaves Black other options. 4...Ba6 attacks c4 at once. The Farago Defense, 4...Ba6 5. Qc2 Bb7, returns the bishop to the long diagonal once White's queen has left d1. Another try is 4...c5 5. d5 Ba6, where the bishop again targets c4 after White gains space. By the mid-1980s many players preferred the order 4. Nc3 Bb7 5. a3, which reaches the main setup while sidestepping both of these ...Ba6 lines. The direct 4...d5 is rarer and has given White good results. The engine rates the position as roughly balanced, and White scores only marginally better than Black in the database.