Defending champion Novak Djokovic booked a 10th straight US Open semi-final appearance when Jo-Wilfried Tsonga retired trailing 6-3, 6-2 in their marquee quarter-final on Tuesday.
It was the third time in five matches that an opponent's injury has worked to Djokovic's advantage, after his walkover into the third round where Mikhail Youzhny retired after just six games.
Ninth-seeded Tsonga gave him more of a workout, but even before an apparent left knee injury began to trouble the Frenchman in the second set Djokovic had the match well in hand.
The Serbian world number one will face another Frenchman, Gael Monfils, for a place in Sunday's championship match after the 10th seed pummelled compatriot Lucas Pouille 6-4, 6-3, 6-3.
It was the first time in 89 years that three French men had reached the quarter-finals of the US championships.
Tsonga was the highest seed among them, but his challenge ended with a whimper.
Down two breaks at 2-5 in the second, he called for the trainer, wincing as his knee was manipulated.
A merciless Djokovic then served out the set at love, firing a 118 mph (189.9 Km/h) ace -- his first of the contest -- on set point.
After Tsonga opened the third set with a double fault he called a halt.
"I really wish Jo a quick recovery," Djokovic said. "He's a fighter, he's somebody that loves the big stage."
But Tsonga wasn't able to shine on that stage. Despite an entertaining array of shots, the longer the rallies went the more he missed, his unforced errors eventually climbing to 37.
He gifted a break to Djokovic with three double faults to fall behind 2-4 in the opening set, and while he regained the break he dropped his serve again in the next game and suddenly Djokovic was serving for the set.
A break for 2-1 in the second was the only opening Djokovic needed. He backed up the break with an emphatic hold at love, broke again for 5-2 and didn't face a break point in the second frame.
It was an encouraging performance for a player who arrived in New York off a third-round exit at Wimbledon and a first-round exit at the Rio Olympics.
Although he won the Toronto Masters, he pulled out of Cincinnati with a left wrist injury.
"I thought that I came out with the right intensity," Djokovic said.
"The quality of my game and level of performance has risen in last couple of days, which obviously encourages me prior to the last four.
"I put myself in a position again to be one match away from the finals. As the tournament progresses, I feel like I'm getting better."
In Monfils, 12-time Grand Slam champion Djokovic will face a player whose only prior semi-final run at a major came back in 2008 at the French Open.
Monfils was in control throughout against the 22-year-old Pouille, who was coming off an epic fifth-set tiebreaker win over 14-time major winner Rafael Nadal.
That marked the 24th-seeded Pouille's third straight five-setter. Whether it was a let-down after the biggest win of his career or sheer fatigue, his 44 unforced errors meant he never stood a chance against a dialed-in Monfils.
"Of course I was a bit tired today," Pouille said. "It would have been better if I played a bit less time on court. Gael was playing very good. He was better than me today."
Dictating from the baseline, Monfils took charge with seven of his 13 aces in the opening set, gaining the only break he needed in the seventh game.
Pouille conceded a break with a stream of errors to fall 1-2 down in the second, and a break of more than 15 minutes to close the new Arthur Ashe stadium roof, with Monfils up 4-3, did nothing to change the momentum.
After holding with back-to-back aces, Monfils broke the error-prone Pouille at love to take the set.
"I was lucky because I had a break so it was easy in my mind," Monfils said of coping with the delay. "I just felt so good (and) it was going to be even better because it was going to be indoors. I just kept going with my game plan."
One break was all he needed in the third, as he wrapped up the match without facing a break point.
The remaining quarter-finals take place on Wednesday with Wimbledon and Olympic champion Andy Murray of Britain facing sixth-seeded Kei Nishikori of Japan and third-seeded Stan Wawrkina of Switzerland facing Juan Martin del Potro, the 2009 champion whose career was nearly derailed by a series of wrist injuries.
Meanwhile, Caroline Wozniacki's dramatic resurgence continued Tuesday when the former world number one defeated a hobbling Anastasija Sevastova to reach a fourth US Open semi-final.
The two-time runner-up, ranked at a lowly 74 after an injury-hit campaign, eased to a 6-0, 6-2 win and will face second seed Angelique Kerber for a place in Saturday's championship match.
Sevastova, playing in her first Grand Slam quarter-final, never recovered from falling and turning her right ankle in the second game of the opening set.
The 26-year-old was hobbled from that point on and the contest was over in just over an hour with the world number 48 having committed 30 unforced errors to the Dane's five.
Wozniacki, the finalist in 2009 and 2014 and semi-finalist also in 2010 and 2011, sympathised with Sevastova after she spent almost three months out of the sport with a right ankle injury earlier this year.
"I feel really sorry for her as I have had that injury before," said 26-year-old Wozniacki who will now return to the top 30 as a result of her surprise run in New York.
"I had to keep pushing her back and make her move."
Sevastova, the Cinderella story of the US Open after she had retired in 2013, won just 12 points in the first set before she briefly rallied late in the match.
Even having her right ankle heavily strapped did nothing to improve her chances of becoming the first Latvian woman to reach the last-four at a Grand Slam.
"It was tough, but what can I do? I tried my best. I don't like to retire, but Caroline played great tennis. Even if I had no injury it would be tough to beat her," said Sevastova.
Australian Open champion Kerber defeated Italy’s Roberta Vinci 7-5, 6-0 to reach her second semi-final in New York having also made the last four in 2011.
Kerber holds a 7-5 career record over Wozniacki.
The German second seed showed remarkable powers of resilience to retrieve three breaks of serve against Italian 33-year-old Vinci in the first set.
In a powerful demonstration of her title credentials, 28-year-old Kerber then wrapped up the second set of her quarter-final by allowing Vinci just five points on her serve.
"It's always tough to play Roberta, she always comes out to play great tennis," said Kerber, who last made the semi-finals in New York in 2011.
"I am happy to win in two sets which means a lot to me."
Kerber could dethrone Serena Williams, who she has already faced in the Australian Open and Wimbledon finals this year, on top of the world rankings if results go her way.
"I remember the semis in 2011. That was maybe a little bit of surprise. I had nothing to lose and I just played great tennis," she said.
"Now I'm a completely different player. I have a lot of confidence and I know how to win big matches."
Vinci, bothered by a foot injury this tournament and playing with her left calf strapped on Tuesday, was ahead with a break on three occasions in the opening set for leads of 1-0, 3-2 and 5-4.
But Kerber kept reining her in and with the seventh break in 12 games, the German took the opener after 54 minutes when Vinci was called for a foot fault.
The Italian aimed sarcastic applause and a thumbs-up at the impassive line judge, but the veteran never regained her composure as she garnered just 10 points in a 24-minute second set.
Vinci, who has yet to decide on whether or not she will continue to play in 2017, admitted Kerber was the better player in the important moments.
"She's on fire. She's won a lot of matches. When the moment is tough and both players are so close, she's focused. She's in good shape. She's No. 2. So probably this is the difference between us," said Vinci.
The remaining quarter-finals take place on Wednesday with world number one Williams facing fifth seed Simona Halep of Romania and Croatian teenager Ana Konjuh facing fellow big-hitter, Karolina Pliskova of the Czech Republic.