Tactical shot leads to uncertain ending

In my last club game I had the White pieces and played e4. My opponent elected to play the sicilian ... I played the closed variation with 2.Nc3, hoping to get a Grand Prix Attack. Interestingly my opponent elected to play 4...Nf6? which although not a blunder, seems not to be a 'book move'? I'm not sure what his intention was but I will be putting the game through Fritz at some stage ...

As the game progressed it it turned into a classic fight for the center and the e5 pawn became the focus. After some analysis in the curry house afterwards an IM colleague had a look at the game and noticed that Black can actually win a pawn but I can't see where? Another candidate game for Fritz!!

(I found out after the game that my opponent was graded almost 300 Elo points above me at 1840 Elo. This game had a sharp conclusion which led to uncertainty and served me well!)

As usual, any comments welcome ...

Chess Diagram 1 - Closed Sicilian - 2.Nc3

1. e4 c5 2. Nc3 Nc6 3. f4 e6 4. Nf3 Nf6 5. e5 Nd5 6. Nxd5 exd5 7. Be2 Be7 8. O-O O-O 9. b3 d6 10. Bb2 Bf5 11. c3 f6 12. d4 Qd7 13. Bd3 Be4 14. Re1 Qf5 15. Bxe4 dxe4 16. Nd2 d5 17. Rf1 fxe5 18. fxe5 Qe6 19. Qe2 a6 20. Rad1 Rae8 21. Rxf8+ Rxf8 22. Nxe4 ( 22. Nxe4 dxe4 23. d5 ) 0.5-0.5

Note: I offered a draw in this position and it was duly accepted.

PGN Viewer courtesy of http://chesstempo.com/