Fusilli: Instructive endgame!
White to move:
click for larger viewWhen I was a kid, my club teacher used to tell us "make first the move that you will always make." That deserves to be among the most celebrate chess quotes, but I've never seen it anywhere. In my experience, it proves to be correct quite often. In this position, the move that White will always make is Kf4, so why not make it now? It's the winning move. But White here played 39.c4? Black responded 39...a4? and lost. But Black had the draw within reach with 39...bxc4! 40.bxc4 d5! although it was pretty hard to see. 
click for larger viewIf 41. Nf4+ Ke5 42. cxd5 a4 43. Kf3 Kd4 44. Ke2 Ke4 
click for larger viewNow 45.Nh3 Kxd5 46.Kd3 Ke5!
click for larger viewThe computer says white is overextended and cannot avoid the draw. Well, actually, the computer just says 0.00, but that's what I think it means! Again, this is the quick and dirty Stockfish... but one can see that winning would be quite a challenge. One can imagine the white knight will have to be sacked to stop the f-pawn while the white king goes kill the a-pawn but will not have enough time to kill the c-pawn too before the black king is over the b-pawn. If, instead, 41.c5 a4 42.Kf4 d4!
click for larger view43.Nb4 Kf6!
click for larger view... it appears white cannot make progress. If 44.Nd5+ Ke6 45.Nxc7 Kd7, the white c-pawn will fall and the black king will secure the trade of the a and b pawns. Maybe someone wants to check with a more serious computer analysis? In any event, I remember my teacher today and his "make first the move that you will always make" and once again cherish his advice. | 
Kibitzing
sac: 49.Nxd5+
