Just when the US Open is getting down to the crucial matches, world No 1 Novak Djokovic found himself in a flawless zone that even he rarely reaches to put himself in the quarterfinals.

The six-time Grand Slam champion from Serbia routed Spain's 43rd-ranked Marcel Granollers 6-3, 6-0, 6-0 in only 79 minutes at Arthur Ashe Stadium.

"It's a great joy," Djokovic said. "It's a fantastic feeling when you're playing this well. You love spending time on the court and experiencing such a great zone where you are at that moment."