I recently won a game at chess.com in which my queen and knight combined to mate. My opponent was Qais71 of New Zealand who played black. Here are the moves of the game along with my commentary:
1. e4 d5
2. exd Qxd5
This opening is known as the Scandinavian Defence. Black has an open d-file but the queen comes out early.
3. Nc3 Qd8
This retreat by black is not the best. A more popular move is Qa5.
4. Nf3 g6
5. Bc4 Bg7
6. 0-0 e6
Black protects the f7 square.
7. Re1 Ne7
Here it is more common for black to play Nf6. He probably wants to keep the diagonal open for the bishop on g7.
8. d3 0-0
9. Be3 b6
10. Qd2 Bb7
I do not want black to capture my knight and destroy the pawn structure around my king.
11. Ng5 a6
12. Bxe6 Qd6
Black does not accept my bishop sacrifice because I can then play Nxe6 which forks his queen and rook.
13. Bxf7+ Rxf7
I take the pawn to further expose the black king.
14. Nxf7 Kxf7
White has an extra piece but I have two extra pawns and the black king is exposed.
15. Bh6 Kg8
Black does not want the white queen on h6.
16. Bxg7 Kxg7
17. Qe2 Nf5
18. Ne4 Qc6
I cannot move my knight on my next move because then black can mate.
17. f3 Nd7
Black finally frees his rook on a1.
18. Ng5 Nf6
19. Ne6+ Kh6
20. Qd2+ g5
After my twentieth move, mate is unavoidable.
The keys to victory in this game are my protected king, ability to expose the black king and coordination of my knight and queen. Black has a material advantage but it is of no consequence. My pieces are better developed than his.