World number one Novak Djokovic has insisted that there are aspects of his game that he needs to improve on despite advancing to the fourth round of the US Open on Sunday.

The Serb moved on from the third stage of the tournament after cruising past Joao Sousa with a 6-0 6-2 6-2 win at Flushing Meadows.

"I am not obviously as comfortable on the net as I am on the baseline, but I've been working on it," Djokovic told reporters. "It's part of my game that I still need to improve. I'm aware of that.

"It makes me happy that I have room for improvement, and I keep on spending hours and hours on the court and working on variety in my game.

"And serve, especially that part of my game. I want to try and get as many free points on the serve as possible."

Djokovic was beaten in the final at the US Open last year by Andy Murray.