The French number one claimed just three games as Djokovic advanced to the semi-finals with a 6-2 6-1 victory in Montreal.
"[Djokovic] was not missing at all. I was gaining no free points on my serve," Monfils told reporters.
"He was certainly the best Novak I have ever met. He was always perfect, perfect, perfect."
Djokovic has now won all seven meetings between the two players.