Novak Djokovic brought an end to the run of German qualifier Jan-Lennard Struff as the 24-time Grand Slam champion eased into the US Open quarter-finals on Sunday.

The 38-year-old Djokovic coasted past world number 144 Struff 6-3, 6-3, 6-2 to set up a meeting with Taylor Fritz, the last American left in the men's draw and 2024 runner-up.

Djokovic was in cruise control throughout and broke the 35-year-old Struff five times but again showed signs of wear and tear as he received treatment to his shoulder at multiple changeovers.

"It definitely helps if you serve well. I think I had a great serving performance last round and also tonight," said Djokovic. "That helps make it easier on the court."

Seventh seed Djokovic has reached the last eight at Flushing Meadows for the 14th time. He is through to a 64th Grand Slam quarter-final in his 80th appearance at this level.

Djokovic has won all 10 matches with Fritz including a straight-sets victory in the quarter-finals two years ago when the Serbian star captured his most recent major. (AFP)