We continue the game, starting from the following position.
White has to create some new weaknesses in Black's position. The way to win (when you've reached a superior position) is to play against multiple weaknesses.
The backward pawn alone isn't enough to win the game.
When there's only one weakness available, you'll have to create a second one.
18...Rc5; 19. Qe3, Be7;
White tries to find the right squares for an attack. Black puts his pieces in a defending position.
20. Rd3, Bd8; 21. Qd2, Rc6;
Now White has pressure against the weak pawn, but there is no concrete way to win it.
You'll see that Black has a hard time finding good moves.
22. Qd1, Kg8;
23. h4, Kg7;
Black plays wait and see. He might have done better by playing h5 (to stop White's next move).
24. h5, Bg5;
25. Qf3, Rc8;
Now White will reposition the rook.
26. Rd1, Rc6;
27. Qe2, Rc8;
There's not much happening on the d-file, so White is going to try something else.
28. Rh1, Kg8;
29. f3, Rb8;
With f3, the white queen has access to f2. This makes Qa7 a possibility. Another idea is to play the queen to h2.
30. Qf2, Rb7; (preventing Qa7)
31. hxg6, fxg6;
The position is opened up now. The open lines and diagonals favour White.
32. c5!, dxc5;
The weak pawn is gone now, but it's traded for an attack.
33. Qxc5, Bd8;
34 Rc1, Kf7;
White keeps finding smal threats. This makes blacks life difficult.
Black still has no useful moves. He tries to hold on by achieving the best defensive setup after each threat. He can only defend.
38. Rc6, Rd6;
39. Rc8, Qd7;
40. Qc5, Kh6;
41. Rb8, Bf6;
42. Qe3+, Bg5?;
Black's position was already very difficult to play, but his last move was a mistake.
It shows that even a world class player like Anand makes mistakes when he has to defend for a long time.
43. f4, exf4;
and Black saw the end coming so he called it a day.
After 44...Kg7; 45. Qd4+,
45...Bf6; 46. Qxf6+,
46....Rxf6; 47. Rh7+,
47....Kxh7; 48 Nf6+, Kg7; 49 Nxd7 and wins
A weak pawn may be used to get the upper hand in a game.
The weak pawn can be attacked, the square in front of the pawn used as an outpost.
This doesn't assure the win, but it may give you a very good position.
When you're able to create a second weakness (a lot of manouvring may be called for), the play against two weaknesses may win the game, all because of the weak pawn.