Lesson
Black to move. Main line: 25... Re6 26. a4 Ne7 27. Bxe6 fxe6 28. Qf1 Nd5 29. Rf3 Bd3 30. Rxd3 cxd3
25...Re6 does not force an immediate tactic. It places the rook where White’s dark-squared bishop can take it, because that bishop is the piece most capable of supporting the e5 and d4 pawns and challenging Black’s blockade.
After 27.Bxe6 fxe6, Black has given rook for bishop but gains a compact pawn center and the d5 outpost. The knight reaches d5, the bishop enters d3, and the c-pawn recaptures on d3 to leave White’s pieces tied to passed and protected pawns.
The game was eventually drawn, which is part of the lesson: a brilliant move can be the only practical way to neutralize an advantage. Petrosian evaluated activity, color complexes and blockade more accurately than a simple material count.