Mate with Queen and Knight

In a game of speed chess, I mated my opponent with my queen and knight. My opponent, Grenouille of Ireland, played black. Here are the moves of the game along with my commentary:

1. e4 e5
2. Nf3 Nc6
3. Bb5 Qf6

Black brings the queen out early.

4. 0-0 a6
5. Ba4 Nge7
6. c3 d6
7. h3 Bd7

Now black has the option of castling queenside.

8. d4 exd
9. cxd h6
10. e5 dxe

With the black king in the centre, I decide to open lines of attack.

11. dxe Nxe5
12. Bxd7+ Nxd7
13. Nc3 0-0-0
14. Be3 g5
15. Bd4 Qg6

I skewer the queen and rook.

16. Bxf8 f6
17. Qd4 Qg8

Black makes a mistake. He wants to capture my bishop, but now the pawn on f6 can be captured with Bxf6.  A better move for black is Ne5. Though I can play Bxf6, I make a different move.

18. Qa7 Qxh8
19. b4 Nc6
20. Qa8+ Ncb8

Ndb8 gives the black king another escape square.

21. b5 Nb6
22. Qa7 N8d7
23. bxa bxa
24. Qxa6+ Kb8

The black king is too exposed.

25. Nb5 Nc8
26. Rab1 Bc5
27. Na7+ Bb6
28. Nc6#

My knight and queen combine to give mate.

Black has nearly as much material as white, but he loses because his pieces are all on the back rank, they are uncoordinated and his king is too exposed.  Though he brings the queen out early, she does not play a big role in the game. On h8, she is too far to defend her own king and too far to attack the enemy king.