Austrian seventh seed Dominic Thiem reached the French Open semi-finals for the third successive year with a straight-set win over an injured Alexander Zverev.
Thiem, 24, won 6-4 6-2 6-1 against the German second seed.
Zverev, 21, struggled with a hamstring injury from midway through the second set, needing treatment and heavy strapping before continuing.
But he cut a forlorn figure as Thiem triumphed in one hour and 50 minutes.
“He is one of the fittest guys on tour but even for him it is tough to play three five-setters in a row,” said Thiem.
“I hope we have many more matches at this stage or later in a Grand Slam – and we are both 100%. It will be nicer for everybody.”
Thiem will meet Italian Marco Cecchinato in the last four after the world number 72 beat 12-time Grand Slam champion Novak Djokovic in four sets.
Zverev injury ruins highly anticipated contest
Zverev and Thiem have long been identified as the two younger players most likely to threaten Rafael Nadal’s dominance on clay.
Zverev is the leading player on the ATP Tour this year, having earned more ranking points and won more matches than anyone else.
Thiem’s preparations for Roland Garros were boosted by winning a tour title in Lyon, moving him clear of Nadal as the leading man on clay – in terms of number of matches won – this year.
So it was a quarter-final greeted with much intrigue and excitement as both men looked to move a step closer to a potential first Grand Slam title.
Unfortunately the match-up was ruined as a contest when Zverev, playing his first Grand Slam quarter-final, pulled his left hamstring midway through the second set.
Zverev had spent almost two and a half hours more on court than Thiem in his run to the last eight, having needed five sets to come through each of his previous three matches.
That appeared to have an effect on the German as he made a slow start in the first and then pulled up in the second.
He decided to carry on, but looked nothing like the player who had been tipped by some to win Roland Garros.
He won just four points as Thiem raced 4-0 ahead, fighting back briefly by earning a break point at 4-1, but losing serve again in the next game as Thiem advanced with a trademark backhand winner.
Zverev said he thought about quitting because of the injury and would need a scan to determine the extent of the damage before Wimbledon.
“I didn’t want to pull out for the first time of my career in a Grand Slam quarter-final,” he said.
“I knew I wasn’t going to win. I could barely move. I couldn’t serve. I couldn’t really do anything.
“But I wanted to finish the match and give the credit to Dominic. He deserves to be in the semi-finals.”
Time for Thiem to step up
Thiem lost in the Roland Garros semi-finals to Novak Djokovic in 2016 and Nadal last year, acknowledging before his match against Zverev it is “time to make a great step” from being labelled as a future champion to actually winning a major title.
Unlike Zverev, he has never won a Masters title but is hoping to go one further by emulating compatriot Thomas Muster to become the second Austrian man to win Roland Garros.
And he showed signs of his pedigree in an impressive first set.
Thiem dominated his service games, dropping only six points on it, while taking the only break point of the opener with a stunning cross-court backhand.
Although Thiem’s one-handed backhand is regarded as his most potent shot, winners were coming from both sides before he clinched the set with an ace out wide.
However, he did not have to be at his best during the next two sets as his good friend Zverev struggled.
A tough match to watch – analysis
Great Britain Davis Cup captain Leon Smith
Zverev is a popular figure, he’s had an incredible year but it wasn’t really a match. He looked very tired and jaded in the first set and then obviously struggled with his hamstring. It was pretty tough to watch when you see Zverev looking so flat. No doubt there was some mental fatigue as well from playing so many five-set matches.
Thiem won in one hour and 50 minutes and will be fresh in the semi-finals.