Knight to the rescue

My instant reaction to the below problem was Qxh2, as its mate.

Although, of course, it isn't...

Shortly afterwards, the solution dawns. Its not an Arabian mate, but its the next best Knight mate, and its a Queen sacrifice ! What more can you ask ?

Sadly, the problem does not seem to be from an identified game, but still good to see.

Black to play

Material or Mate ?

One thing I enjoy about a blitz game are those occassions when one side has the upper hand, but the other has an immediate riposte, like some "sword of Damocles",  hanging over his opponent.

Usually, this is heightened by the time factor : the attacking side could win easily with enough time to think, but that's the problem !

Here's an example from recent play.

Black is more than ahead in material, but it seems like his Knight is pinned to his Queen, and a lowly pawn is about to regain the piece.

But is there a simple way out ? 

Has Black just lost a piece ?

Yes, there is !  In fact more than one, but the Queen is the better piece to use, and 20...Qc5+ forces Kh1 ( of course, Kf1 is mate with Qf2 ).

20..Qc5+ 

After Kh1, the Knight moves in for a check, forcing Kg1 allowing Knight takes Queen, and prompting a resignation.

21...Nf2+ 22. Kh8  : Mate in 3

However, 22...Nxg4 is not the best move, though of course it crushes White's resolve and the game is over.  

There is a much quicker and more elegant mate in 3, and the clue is in a previous post, if you need it !