Nice fork!

Well, it is only a queen exchange and does not actually win material. But it is fun to do it this way  

I think Black ought to have kept his K in the centre: 24...Ke6 25.Nxe4 Rd8, with 26...Kf5 to come. With such an active King, compared with White's, Black ought to hold this endgame well enough. However, Black's following move, by depriving his knight of protection from b7 is going to make the passed pawn much harder to hold.

More aggressively exploiting Black's previous is 26.Rc1.

Wouldn't that risk losing the pawn at h7? Say if 27. ... d3, 28 Ng5 Kf6, 29 Nxh7+. Sure, some moves for black prevent it, like 27 Rd7, and some counterattack like 27. Nb4, but ultimately, it seems that the white knight can cause trouble on g5 if it's not prevented.

Oh, I see that now  

Not too late though.

This could have been stopped by a timely ...Ne5.

Black could just about force a draw here: 31...Ne5+ 32.Ke4 Re8! The d-pawn is inviolable: 33.Kxd4 Rd8+ -/+; 33.Rxd4 Nc6+ -/+. But what can White do about the threatened discovered check? The King has but one move: 33.Kd5 Rd8+ when 34.Ke4 is forced.

Looks like a good idea, although some lines after Re1+ look fair for White.

32...Na5? is the mistake that goes a long way to losing Black the game. Better is 32...Rd6?! but White still gets slightly the upper hand after 33.Re1+ Kd5 34.Nf5 Rd7 35.Re4 after which 35...Ne5+ might limit the damage (36.Kd2 Nc4+ 37.Ke2 Rc7 38.Rxd4+ Ke5 39.g4 Nxb2 - unclear). But probably best is simply 32.Kd5, which also keeps closed the c-file. Now, after 32...Na5?? White could have caused Black a whole deal of trouble by 33.b4! Nb7 (Not 33...Nb3??) 34.Rc7 etc.

But White had very fair winning chances with 37.Nf5+ Kc4 38.Nxh6. True, Black's d-pawn remains dangerous, but with care and patience White ought to be able to contain it and gradually set about getting his own pawns into motion. This is - or would have been - a very fascinating endgame. After this knight 'sac' White stood to lose (37...dxe2 38.Kxe2 Rd6! protecting the flank pawns, but also threatening to exchange rooks, e.g. 39.g3!? Re6+ 40.Rxe6 Nxe6 and White's chances don't look very promising).

I am inclined to say refused, but then my philosophy is never to assume that my opponent has made a mistake. But in such an endgame I would keep the passed pawn, not the knight. If it were a bishop I might say differently...

id=fatcat2 is correct in never assuming your opponent has made a mistake. But the converse holds equally true: don't trust your opponent! If you can't find a reason not to play a move that you would like to play: play it. This is "show me" country. Black probably feared what he couldn't find against 37...dxe2 and chose something else. But, unable to find for himself any refutation for 37...dxe2, he would have been quite right to say (to himself) "Show me!", and taken the knight.

Agreed. I missed taking an opponent's Q recently because I "trusted" him. I didn't even see the mistake till the following move, when, amazingly, the Q was still en prise. I'd have nabbed this knight, assuming I'd seen the opportunity!