In the game above, White played 18. gxf3? resulting in a draw by perpetual check.

He missed the spectacular defence 18. Rg1! Ng3+ 19. hxg3 Qxg3 (threatening Qh3#) 20. Qh6!! gxh6 21. gxf3! and wins.

This puzzle was taken from Unbeatable! by Jan Werle: you can read my review of this book here.