Position 1 after 17Nd3;Black to play
Karjakin
Carlsen
Carlsen just played 17Nd3
Solid position for white, controlling center and d5 square.
Karjakin tried to attack with..h5
Position 2 after 34Nb5, Black to play
Karjakin
Carlsen
Here Black should play 34..Ra1 and its not clear what White should do. 35 Ra1 or 35 Kh1 waiting;
Instead 34..Rb3?! ran into 35 Nd4 forking Rook and Queen. White gains the exchange while still being in control
Black to play after 48 Kh1
Karjakin
Carlsen
Here Black played 48..Qf2?? which ran into 49Rc8+ Kh7 50 Qh6+!! Kh6 51 Rh8 Checkmate or gh6 51 Rf7 Checkmate
Black had to exchange queens but ending is riskless for white. The critical mistake was to sacrifice the exchange on move 34; 34..Ra1 was the only way to keep the game going for Black.
The final combination is easy to spot, and it is possible Karjakin saw it but went for anyway.