1. d4 Nf6 2. Nf3 e6 3. Bg5 d5 4. Nbd2 Be7 5. e3 Nbd7 6. Bd3 c5 7. c3 b6 8. O-O Bb7 9. Ne5 Nxe5 10. dxe5 Nd7 11. Bf4 Qc7 12. Nf3 h6 13. b4 g5 14. Bg3 h5 15. h4 gxh4 16. Bf4 O-O-O 17. a4 c4! Let's analyze this position a bit. The players have castled opposite wings so this announces a sharp game. It's a race who will get to the opponent's king first. At the moment, black managed to open g-file for his rooks and in general stands better, especially after 17. .. c4! With that move, black is trying to keep the position closed on queenside where white is going to attack and meanwhile he will prepare some counter-attack on kingside.
18. Be2 a6! Another good move that is meant to deal with both white's moves b5 or a5. If white will play b5 now, black will answer with a5 totally closing the position and in case of a5, black will answer with b5. Therefore, it seems that white's attack has come to a dead end.
19. Kh1 Rdg8 20. Rg1 Rg4 Black occupies the semi-open file and is ready to double rooks putting pressure on g2 pawn.
21. Qd2 Rhg8 22. a5 b5 23. Rad1 Bf8 24. Nh2 This is the crucial moment of the game. Black rook on g4 is under attack. What to do? To retreat with that rook on g7 or g6? Petrosian decided not to do that. Instead he played:
24... Nxe5! He is willing to sacrifice an exchange, but as compensation he will create a strong mobile group of pawns as we will see immediately.
25. Nxg4 hxg4 26. e4 Bd6 27. Qe3 Nd7! Good move wi th idea to clear e5 square for future pawn advance. Black's plan is just to play e5, f5 etc.
28. Bxd6 Qxd6 29. Rd4? A bit weird move which I can't understand. Better was maybe 29. Qh6 although after 29Qe5 white's position remains inferior.
29... e5! 30. Rd2 f5! Now this is a nice view! Look at black pawns ready for charge. Those are called mobile group of pawns. Just look how they limit all white's pieces activity and on the other hand give black huge space advantage. Black's idea is just to push those pawns forward and get an attack on white king.
31. exd5 f4 32. Qe4 Nf6 33. Qf5+ Kb8 34. f3 Bc8 35. Qb1 g3 The circle is getting tighter and tighter with every move. That mobile group of pawns are amazing.
36. Re1 h3! It is time to open h file towards white king and also to create a strong protected passer on g3! Let's watch how Petrosian converts his advantage.
37. Bf1 Rh8 38. gxh3 Bxh3 39. Kg1 Bxf1 40. Kxf1 e4! Look at those pawns going! Petrosian sacrifices another pawn in order to get two very strong passers on "f" and "g" files. So practically white cannot take on e4.
41. Qd1 Ng4!! The move is based on same motif. If white will take on g4, black will create f-g phalanx with 42f3 followed by Qh6 and mate is coming.
42. fxg4 f3 43. Rg2 fxg2+ and here white resigned, because of 44. Kxg2 Rh2+ and g pawn is unstoppable.