Unnaturally tough resistance brings Kamsky victory

In annotating the final game of the Kamsky-Topalov match for ChessBase, Alejandro Ramirez wisely writes, "In most cases in chess, the position is as natural as it seems."  In other words, most of the time, natural moves are sufficient to win a won game.  Only the strongest players have the fighting spirit to offer maximum resistance even when the game is objectively lost. 

Acccording to the computers, Gata Kamsky was hopelessly lost.  But Kamsky drew convincingly, without an obvious blunder by Topalov.

Veselin Topalov-Gata Kamsky

2011 Candidates Match, Kazan, Round 4

After 42...Ke8: White to play

What would you play as White?  How deeply would you calculate?

Veselin Topalov-Gata Kamsky

2011 Candidates Match, Kazan, Round 4

After 49.Qd8: Black to play

Black has several reasonable tries here (and perhaps more than one way not to lose), but only one move is clearly best.  Can you find it?

Congratulations to Gata Kamsky!  Later this week, he'll be facing Boris Gelfand, who has many friends in Chicago himself.