Guarding champion Novak Djokovic is through to the US Open semi-finals after a knee damage constrained Jo-Wilfried Tsonga to stop when trailing 6-3 6-2.

Djokovic, 29, has finished only two of five matches in New York, profiting from a walkover and two retirements.

He will confront another Frenchman in the last four after Gael Monfils beat comrade Lucas Pouille 6-4 6-3 6-3.

"This was the situation that I required and I longed for," said Djokovic, who has confronted his own wellbeing issues.

The Serbian world number one touched base at Flushing Meadows nursing wounds to both his left wrist and right elbow.

"I got a great deal of days off and recuperated my body," he said. "At this moment I'm feeling near the pinnacle. That is the position where I need to be."

Second seed Andy Murray goes up against Kei Nishikori on Wednesday, before Juan Martin del Potro and Stan Wawrinka play the remainder of the quarter-finals.

In the ladies' draw on Tuesday, Denmark's Caroline Wozniacki beat Anastasija Sevastova 6-0 6-2 in another match defaced by damage, with the Latvian extremely hampered by a contorted lower leg.

Wozniacki won effectively to set up a semi-last against German second seed Angelique Kerber, who beat Italy's Roberta Vinci 7-5 6-0.