The World No.1 was comfortably in charge of Jo-Wilfried Tsonga when his opponent pulled out with a knee injury to confirm his place in the final four .
Novak Djokovic is through to the US Open semi-finals for a 10th consecutive year after Tsonga retired with an apparent knee injury one point into the third set trailing 6-3, 6-2, 0-15, marking Djokovic’s third passage by default in four matches since a first-round win over Jerzy Janowicz.
That means the defending champion is into the last four having played a total of 84 games – and only nine complete sets – with less time spent on court (6hr 26min) than most transatlantic flights.
The primrose path includes a second-round walkover by Jiří Veselý, the young Czech who’d beaten Djokovic in Monte-Carlo in their lone previous meeting, followed by retirements by Mikhail Youzhny in the third round and Tsonga in Tuesday night’s headliner.
Djokovic believes that he is now reaching the peak in terms of his form, and has no concerns over a lack of rhythm at the business end of the competition.
“I am not really concerned,” Djokovic said.
“Actually, in this stage of the season, considering some physical issues I have had in the last month, month and a half, this was the scenario that I needed and I wished for.
“I got a lot of days off and recovered my body. Right now I’m feeling very close to the peak. That’s the position where I want to be. This scenario was ideal at this stage.”
Djokovic will now face Monfils, who has advanced to his first Grand Slam semi-final since 2008, and will enter as heavy favourite, having won each of their last 12 meetings.
“I love watching Gael,” Djokovic said. “He’s one of the few players that I will definitely pay a ticket to watch.
“He’s very charismatic. Plays with a smile. Enjoys tennis. Enjoys life. But also he seems more focused at this time of his career.
“Especially on the hard court this year maybe he’s playing the best tennis he ever played. I’m definitely expecting a tough battle.”