"I'm trying to enjoy the efficiency of my serve," the Serbian, who hit 12 aces during the match, told reporters.
"I'm not very well known around the tour for big serving. But so far in this tournament, and also in Beijing, it has been working very well for me.
"It has been giving me a lot of free points, a lot of confidence in the matches."
Djokovic's reward for beating Lopez is a quarter-final encounter with German veteran Tommy Haas.