He was in great form on Monday when defeating Viktor Troicki 6-2, 6-2 to reach the fourth round.
In a chat to media after his win, Nishikori felt that he was playing close to perfection in Miami.
"I was almost perfect on the court. It is so exciting that I am playing well here.
"Maybe he was hurting a little bit, but I was still putting him under pressure with my return," he added.
The world number five faces David Goffin next for a place in the quarter-finals.