US Open champion Dominic Thiem said he was "over the limit" physically in his five-hour 7-6 (7-1) 5-7 6-7 (6-8) 7-6 (7-5) 6-2 loss to Diego Schwartzman in the French Open quarter-finals.
Austrian Thiem beat Hugo Gaston in the last round in another gruelling five-set encounter, and simply ran out of steam against the Argentine.
"In the end I gave everything I had out there," Thiem said.
"It was an amazing match - I think the first in my career over five hours."
The start of the two-time finalist's French Open run was only two weeks after he won his maiden Grand Slam title at Flushing Meadows.
"It was a pretty short time with the long trip home, jet lag and everything," Thiem said. "Come here, play in pretty brutal conditions. I cannot say it was a bad tournament - I'm pretty happy about it."
The match, played in blustery weather, featured numerous long rallies, with both players breaking each other several times because of their superb return games.
The first four sets were tight before Thiem's level dropped in the decider, while 12th seed Schwartzman reached his first major semi-final and will now face Rafael Nadal.
The Spanish defending champion, seeking a 13th title, beat Jannik Sinner in straight sets on Philippe Chatrier.
Schwartzman said: "So this win is very important for me. In the second and third sets, I was going a little crazy and I was screaming at myself because I had so many chances.
"But come on, I deserved to win."
Pair serve up mesmerising encounter on Philippe Chatrier
Schwartzman had beaten Thiem only twice in their past eight encounters, but arrived at Roland Garros having reached the final of the Italian Open.
He looked far fresher than Thiem in the opening stages and, after breaking back in the sixth game, ran away with the tie-break.
Third seed Thiem has incredible powers of recovery, though, as demonstrated in the final at Flushing Meadows and in his previous five-setter against Gaston.
There were early breaks in the second set before a 15-minute ninth game where Thiem had seven breaks of serve but failed to convert any of them.
Schwartzman perhaps would have had two break points himself in the next game had he made a relatively easy shot at the net, and was punished for his profligacy as Thiem broke once more before serving out for the set.
The third set was as keenly fought with eight breaks of serve - it was eventually settled once more on a tie-break.
Neither player's level had dropped by the time of the fourth set. Schwartzman looked to have made the decisive break to go 3-2 ahead but he was broken back in the 10th game as he served for the set.
In that game, Thiem underlined why he is regarded as having one of the best forehands in men's tennis with a stunning shot down the line, which had Schwartzman looking on in disbelief.
Again a tie-break decided the set, but this time it was world number 14 Schwartzman who came out on top.
He remained dominant in the decider, breaking to love in the sixth game to go 4-2 up before sealing victory with another break, following five hours and eight minutes.
The 5ft 7in player turned around to the crowd, took off his cap and produced a beaming smile after his greatest achievement at a Grand Slam.