Nimzo-Indian Defense: St. Petersburg Variation

What Is The St. Petersburg Variation?

4...b6 fights for one square: e4. The bishop heads to b7 or a6, and with the pin on c3 it takes the light squares White needs for e3-e4. Every game turns on whether White forces e4 through or Black freezes it, because the bishop pair White wins after ...Bxc3+ is worth nothing behind a blocked center. On a6 the bishop hits c4 and costs White a move: b3, Qa4 or Ng3.

White answers with Nge2 rather than Nf3: after ...Bxc3+ the knight recaptures, so the structure stays clean and White prepares a3 and e4. Calling 4...b6 slow is the error. Black gives up the bishop pair by choice and gains time against c4, and once White pushes e4 with pawns intact, the space wins.

What Do Players Choose At The Decision Point?

Move	Share		Games
O-O	34%		99
c5	20%		59
Bxc3+	15%		43
b6	13%		39