Frenchman Jo-Wilfried Tsonga has become the third of Novak Djokovic’s opponents to have his US Open run ended by injury, handing the Serb a spot in the semi-finals.
It is the nighth-straight final-four berth for reigning champion Djokovic, but this may be the easiest path he has taken.
Djokovic has completed just nine sets in the tournament and played just 84 games.
For comparison, his next opponent, 10th seed Gael Monfils, has won all his matches in straight sets but played 144 games through five clashes.
Monfils beat fellow Frenchman Lucas Pouille 6-4, 6-3, 6-3 to reach his second career grand slam semi-final and first since the 2008 French Open.
After winning a tough four-setter against Poland’s Jerzy Janowicz in the first round, Djokovic was handed a walkover win in the second round when Jiri Vesely succumbed to an arm injury before the match.
Round three was hardly more of a challenge for the world number one, with Russian Mikhail Youzhny calling quits due to a thigh strain after just six games and 31 minutes on court.
Djokovic then powered past 21-year-old Briton Kyle Edmund to reach the quarters, where ninth-seeded Tsonga dropped the first two sets 6-3, 6-2 before retiring with a knee injury.
“I have to say again, I really wish Jo a quick recovery,” Djokovic said.
“It’s never nice to be on the court in the quarter-final of a slam and retire.
“He’s a fighter, somebody who loves the big stage. This is something I’m sure he didn’t hope for.”
In-form Wozniacki ends injured Sevastova’s run
It was not just the men’s side of the draw that was derailed by injury, with Caroline Wozniacki taking advantage of Latvian challenger Anastasija Sevastova’s ankle ailment to set up a semi-final against Angelique Kerber.
Kerber beat last year’s runner-up, Roberta Vinci, 7-5, 6-0 before Wozniacki powered past a hobbled Sevastova to win 6-0, 6-2.
Sevastova had never been past the fourth round of a slam, and her best result in New York were second-round berths in 2009 and 2010, but her run this year was one of the best storylines of this year’s tournament.
The world number 48 overcame world number three Garbine Muguruza in the second round and 13th-seeded Briton Johanna Konta in the round of 16 and had not dropped a set ahead of her showdown with former world number one Wozniacki.
But the 26-year-old rolled her ankle early in the first set and was clearly labouring after a lengthy medical timeout.
Wozniacki, who was runner-up at Flushing Meadows in 2009 and 2014, said she felt “really sorry for [Sevastova]”, but used the injury to her advantage.
“It happened early in the match and then I kept pushing her back and tried to make her move,” the Dane told ESPN court-side.
The in-form world number 72 has not lost a set since dropping her first of the tournament 4-6 to Taylor Townsend, and will need every ounce of her ability when she meets another of the tour’s best athletes in the semi-finals.
Australian Open winner Kerber is eyeing Serena Williams’ world number one ranking and made relatively light work of Italy’s Vinci.
A foot fault on set point in the opening set appeared to trip up Vinci and sent her tumbling out of the year’s final grand slam, with the second set lasting just 24 minutes.
“The key of the match was the first set … it was really close and tough,” said Kerber, who can supplant Williams atop the world rankings if the American fails to reach Saturday’s final.
“She’s a tough opponent with her slice. I was trying to stay in the match and not thinking that I’m the break down.