Novak Djokovic is grateful for the additional rest at the US Open, feeling everything going in the "right direction" despite limited time on court.

The world number one benefited from a walkover in the second round and was on court for just 31 minutes in the third before Mikhail Youzhny retired on Friday.

In total, the Serbian defending champion has needed just over three hours to reach the fourth round at Flushing Meadows.

But, given concerns over wrist and arm injuries, Djokovic said the break may have come at a good time.

"This particular situation I've never had in my Grand Slam career," he said.

"But considering the stage of the season, the amount of matches I've played, what I've been through with my body, I think it's actually good to have some days off and then shorter matches from one side.

"From the other side, sure, as you are approaching second week of the Grand Slam you want to have match play and you want to have time spent on the centre court before you face one of the top players.

"But, again, I'm not too concerned about my game itself. I've worked hard the last couple days.

"Health-wise I feel much better than I did at the beginning of the tournament. I'm confident that everything is going in the right direction."

Djokovic needed four sets to get past Jerzy Janowicz in his opener, while he led Youzhny 4-2 before the Russian retired with a leg injury.

The 29-year-old Djokovic required treatment of his own in the first round, but said his arm was improving.

"The arm is doing very well. Everything, as I said, is going in the right direction. I feel significantly better now than I have just at the beginning of the tournament," he said.

"I'm looking forward to compete."

Djokovic will face Brit Kyle Edmund, who beat American 20th seed John Isner, in the fourth round.