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