Alex de Minaur has rued losing his legs after Russian ironman Daniil Medevdev ended the Australian's US Open campaign with a signature fourth-round victory in New York.
De Minaur played some inspired attacking tennis early to raise hopes of an upset win before the third-seeded 2021 Open champion powered to a 2-6 6-4 6-1 6-2 triumph in oppressively hot conditions on Louis Armstrong Stadium.
Australia's world No.13 had been bidding to make the quarter-finals at Flushing Meadows for a second time but couldn't stay with Medvedev after dropping a tight second set.
"Ultimately, what happened out there was nothing to do with tennis," de Minaur said.
"It was a little bit to do with just physicality. I had a lot of matches this whole summer without a lot of time off and rest, and it seemed to have caught up with me at this moment.
"It's probably the first time in my career that fitness let me down. It's not something that happens. I back myself every day of the year.
"But with all the matches that I played, my schedule, everything, I got to this point and the small margins, small percentages, are pretty big at this stage and level of competition."
De Minaur's departure ends Australia's participation in the singles, with the 24-year-old having to settle for a likely rankings rise to a career-high No.12 next Monday.
Runner-up in 2019 before denying Novak Djokovic a calendar-year grand slam sweep two years ago, Medvedev advances to an all-Russian quarter-final against eighth seed Andrey Rublev.
That didn't look on the cards early against de Minaur, whose aggressive play had the former world No.1 rattled and made a repeat of his win over Medvedev in Toronto last month seem a distinct possibility.
De Minaur won nine of nine points rushing the net and broke Medvedev in the fifth and seventh games to steam through the opening set in 32 minutes.
But a spectacular tweener from Medvedev during a 34-shot winning rally sparked the Russian into action midway through the second set.
De Minaur had to fight off five break points to hold for 2-2 but couldn't recover from 15-40 down serving at 4-5 as Medvedev levelled the match at a set apiece.
The Russian shifted up a gear in the fourth, overpowering de Minaur from the back with two more breaks to take a two-sets-to-one lead.
It was all but over when de Minaur dropped serve twice more in the fourth set as Medvedev surged to 5-1 before closing out the contest after two hours and 40 minutes.
"There was no lack of confidence to beat him. I knew what I had to do to hurt him and I showed it until my legs went away," de Minaur said.
"And then suddenly I had to try and scramble, finding different ways of playing and you can't do that against a player of the calibre of Daniil."
Despite his exit, de Minaur is closing in on a top-10 ranking for the first time and remains a live chance of qualifying for the season-ending ATP finals in Turin.
"I've had some great results and I probably could have been higher (in the rankings)," he said.
"There's still plenty to go - Asia and Davis Cup now. I'm going to be taking the first week of Asia off.
"I need some rest, and hopefully I'll be able to finish the year strong.
"Top 10, Turin; that would be an ideal way to finish the year."
