Know your mates

 It really does help to know mate combinations and be alert to them appearing on the board.

Here, Black played the remarkable 20...f5 ??

..evidently not seeing the back-rank mate !

Same here. 

Qe7+

Black has the choice of Kh8 or Kh6.

Kh8 maybe feels like its bad as it puts the King into a corner, but if you don't know the mate, its not much calculation to see that Kh6 is a worse move and a slightly quicker mate.

After the poor Rf8, White has Nf5+, and Black cannot capture because of the pin so is forced to h5, where Qh4 is mate

Kh8 is , for me at least, a harder mate to see and calculate.

23...Kh8

But if you see the end position, you should be able to work out the mate in 5