Find the Winning Move for Black

[White "anon"]
[Black "talapia"]
[Result "0-1"]
[TimeControl "120+12"]

1. d4 Nf6 2. Nf3 d5 3. c4 Bf5 4. Nc3 e6 5. Bg5 Bb4 6. Qa4+ Nc6 7. Ne5 Bxc3+ 8. bxc3 O-O 9. Bxf6 Qxf6 10. Nd7 Qg6 11. Nxf8 Kxf8 12. Qa3+ Kg8 13. cxd5 exd5 14. O-O-O

This game was played on chess cube a few days ago with a 2+12 time control. Playing a hybrid Marshall Defense with the Black pieces, I lost some material in the opening through carelessness. My saving grace was a focus upon rapid development. The fourteenth move was a critical juncture. See whether you can find the winning move. I have placed the continuation at the bottom of this message.


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[White "anon"]
[Black "talapia"]
[Result "0-1"]
[TimeControl "120+12"]

1. d4 Nf6 2. Nf3 d5 3. c4 Bf5 4. Nc3 e6 5. Bg5 Bb4 6. Qa4+ Nc6 7. Ne5 Bxc3+ 8. bxc3 O-O 9. Bxf6 Qxf6 10. Nd7 Qg6 11. Nxf8 Kxf8 12. Qa3+ Kg8 13. cxd5 exd5 14. O-O-O b5 15. Qc5 Rb8 16. a3 Na5 17. Qxd5 Bb1 18. Rd2 Nc4 19. Rb2 Nxb2 20. Kxb2 Qc2+ 21. Ka1 Qxc3+ 22. Kxb1 b4 23. e3 bxa3+ 24. Ka2 Qb2# 0-1

Alternative mate: Rb2 and then mate by Qc1#

Alternative mate: Rb2 and then mate by Qc1#

That works as well.

21. .. Qc1 was a faster and surer route to checkmate.

The main strategic error of my opponent was to neglect development in favor of pawn-grabbing with the Queen. Castling Queenside was counter-productive as well, and I'm not sure it is possible to pull off such a brazen move in this position. I think he would have won based upon his material advantage if he had not played O-O-O or cxd, but instead a simple g3 to develop the King's bishop and prepare castling Kingside.

Pawn-grabbers take note.