World number one Novak Djokovic has moved into the quarter-finals of a grand slam for the 22nd time in a row after seeing off Germany's Philipp Kohlschreiber in the US Open on Monday.

Kohlschreiber, the 22nd seed, was the last man to deny Djokovic a place in the last eight of a major tournament, beating him in the third round at Roland Garros in 2009, but had no answer this time.

Djokovic made a lightning start, winning the first four games, and although Kohlschreiber began to find some rhythm he could do nothing to prevent a 6-1 7-5 6-4 victory for Djokovic.

Djokovic broke Kohlschreiber twice as he steamrollered his way through the opening set in 25 minutes.

The second set was a much closer affair, and Djokovic was serving to stay alive as he trailed 4-5, 30-40, but a cross-court forehand kept him alive and, buoyed, he swiftly broke Kohlschreiber to go two sets up.

Another unforced error from Kohlschreiber put him in an early hole in the third set, and there was no way back from there.

"It was very humid for both of us," Djokovic said on the tournament website.

"We had a lot of long rallies. The match could have gone either way, especially in the second set."