The former world champion Jose Raul Capablanca preferred a Knight to accompany his queen instead of a Bishop. The Knight can reach both black and white squares and often turns the Bishop into a hopeless spectator like in the final minutes of Game 8.
The knight is also an excellent defender of the king, limiting the enemy queen to long checks. The queen/ knight combo can cover many squares.
The black Knight blocks the pawn on e4 and prevents the bishop from stopping the passed a-pawn. The game will be over in two moves, but what a drama lies in those two turns.
51.Qe6? Carlsen stops the a-pawn advance, but cannot check the black King. He plays defense without offense. Arguably, two moves could steer the game to a draw. [A. 51.Qb7+ Nf7 (51...Kg8 52.Qb8+ Kf7 53.Qb7+ ; 51...Kg6 52.Qa6+ ) 52.Qa8 (52.Qa6 Qc3 53.Qa7 Qb2 54.e5 ) 52...Qc3 53.Qa7 Qb2 54.e5!= ; B. 51.h4 h5 52.Kh3! Ng4 53.Bf3 Qg1 54.Qb7+ leads to a perpetual check.]
51...h5! Surprisingly, White has no good moves. The Black King can hide on h6, if necessary. [After 51...Nf7 52.e5! opens up the Bishop and Black cannot win: 52...Nxe5 53.Bd5= ]
52.h4?! Loses outright. Chess is a cruel game. Sometimes one single square makes all the difference. If the white King stood on h3 already, Black would not be able to win. But now there is not much White can do. [For example after 52.Kh1 Black has two paths to victory: 52...Qc1+ (Opening the position has a pretty point in the line 52...h4! 53.gxh4 Qc1+ 54.Kh2 Qb2 55.h5 (55.Qe7+ Nf7 56.h5 a2 57.h6+ Kxh6-+ ) 55...Nf3+ 56.Kg3 Qe5+ wins.) 53.Kh2 Qb2 54.Qe7+ Nf7 55.e5 a2 56.e6 Qf6 57.Qxf6+ Kxf6 58.exf7 Ke7 ; It is too late to return to the a-file: 52.Qa6 Qc3 53.Qa7+ Kh6 54.Qa6+ Ng6 wins.; Additional point of Black's last move comes after 52.Qf5 Ng4+! 53.hxg4 Qxf5 54.exf5 a2 wins.]
52...a2! A decisive deflection leading to a mating attack. [52...a2! 53.Qxa2 Ng4+ 54.Kh3 Qg1 55.Qb2+ Kg6 the black Queen covers the only reasonable check on b6 and after 56.Bf3 Nf2+ wins.] 0-1