Anand had found an unexpected resource in Bb6 followed by f5, and because of that Carlsen probably should have played c5 instead of Ne4 and got really close to equal.
However it was still slightly imbalanced. Carlsen took considerable risks, and Anand defended really well but missed Ra1+, playing Rc1+ instead. The thing is, it is incredibly hard to sustain that kind of pressure, especially when you are a player, like Anand, who seeks concrete variations all the time.

Carlsen just maintains the position and does not necessarily thinks in terms of "this is a draw", "this should be a win". He plays moves that keep the game going while not worsening his position, and if possible improving it. And he'll keep playing, usually with incredible precision, for as long as there is anything left. Anand played remarkably for many moves, at times more precisely than Carlsen, but it must have drained him.
And this may have been felt in the next game too, when first he was indecisive at a couple of junctions (he had a slight pull initially), then made a few mistakes that were hard to explain practically.

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi