Ulhumbrus: 13 exd5 ?! concedes an advantage in space to Black although Black's centre may become a target instead of a weapon.
The computer prefers 13...Nxd5 to 13...Bxd5. One justification for the former is that it frees Black's f pawn to advance.
14 Ng3 attacks the square f5 whose defender - Black's QB - has been displaced by going to d5.
The computer prefers 14...Qd6 to 14...Bc5 and gives a repetition after 15 Ne4 Qe6 16 Ng3 Qd6. One justification for 14...Qd6 is that it connects the rooks. The text may be a deep and creative idea on Anand's part: It prepares the move ...g6 keeping the N on g3 out of f5 by transferring the bishop to f8. However for this to work, Black has to play the move ...g6. It also costs time.
15 b4 ?! gains space but also creates a target on b4 for Black's bishop.
17...b5? gives White control of the a file and this is going to lead in fact to the loss of the game. This may be Anand's first main mistake. Instead of this 17...Nd7 defends the e5 pawn.
18...Rb8 concedes the a file to White. 18...Bg7 seems consistent and on 19 Nc5 Nd7 attacks the N on c5.
20...Bxb3 draws White's queen on to the a2-g8 diagonal. Instead of this 20...Nb6 defends the bishop and threatens White's a4 pawn.
Instead of 21...Re6, 21...Qe7 prepares ...Qe6 removing White's queen from the a2-g8 diagonal.
Instead of 23...Nf6,23...Qe7 gets ready for ...Kh7 followed by ..f5
24...Nxe4 relinquishes Black's advantage in space. Now Kramnik has a considerable positional advantage. Black seems unable to cover all of his weak spots.
It may be not obvious why 33...Rc8? is an error.
The reason is that after 34 Qa2 White's rook will be able to threaten both Ra8 and Ra7.
In that case Black will want to be ready to obstruct White's rook by ...Rc8 or ...Rc7.
However White can prevent ...Rc7 by Bb6 and that means that the c file is inadequate as a means of defence for Black's rook: Black's rook needs to use the b file instead for this purpose.
This suggests 33...Qc8! 34 Qa2 Rb7 using the b file for Black's rook instead of the a file and now on Ra8 or Ra7 Black has ...Rb8 or ...Rb7. White's bishop cannot keep Black's rook out of b8 so easily.
Perhaps the move 33...Rc8? is Anand's proverbial second main mistake, leading to loss of the game. Although the computer indicates that White's advantage is not that great with best play even after this, the computer may be not as reliable in such positions.