chess online

I'm too lazy to check this with Nalimov TB right now, but if I'm not completely mistaking, black can draw after 4.Kc4:

1. ... Nb1
2. Rb6+ Ka2
3. Rxb1 Kxb1
4. Kc4 Kc2
5. Kb4 Kd3
6. Kxa4 Kc4
7. Ka5 Kc5
...

White has the extra pawn, but it is only a rook pawn.

If white plays

8. a4 Kc6
9. Kb4 Kb6

the black king just has to go to a8 and it's draw.

But if white chooses to keep his king in front of the pawn, not letting the black king get to a8, then black can lock in the king, for example like this:

8. Ka6 Kc6
9. a4 Kc7
10. Ka7 Kc8
11. a5 Kc7
12. Ka8 Kc8
13. a6 Kc7
14. Ka7 Kc8

and as soon as the white king moves out of the a-file the black king gets to a8.

15. Kb6 Kb8
16. a7+ Ka8

Draw!