Sebastian Korda retired with a wrist injury during his Australian Open clash with Karen Khachanov, sending the Russian through to a second consecutive grand slam semi-final where he will meet Stefanos Tsitsipas of Greece.
American Korda has been one of the stories of the tournament, defeating Daniil Medvedev and Hubert Hurkacz to reach a first slam quarter-final 25 years after his father Petr lifted the trophy.
But he began to struggle half way through the second set, receiving a medical time-out, and, after losing seven games in a row, called it quits trailing 7-6 (7-5) 6-3 3-0.
It was a very disappointing way to bow out for the 22-year-old, who was in obvious discomfort and was reduced to chopping forehands in a vain attempt to find a way back into the match.
Having reached the last four at a slam for the first time in his 23rd major tournament at the US Open last summer, Khachanov is now back at the same stage in his next event.
"Back to back semi-finals at a slam feels great," said the Russian. "Obviously not the way you want to finish the match. Up until a certain point it was a great battle."
Khachanov and Korda met for the first time at a grand slam at Wimbledon in 2021, and a topsy-turvy contest went all the way to a fifth-set tie-break before the Russian edged it.
This looked set to be a close battle as well, with Korda recovering from a breakdown to force a tie-break in the opening set and then beginning the second strongly.
But he called the trainer after five games to have his right wrist taped and did not win another game.
Khachanov said reinventing himself as a player had helped him breakthrough to the semi-final stage.
Khachanov burst onto the scene in 2018 when he won the Paris Masters but has had little success since, falling out of the top 10 and reaching only two Grand Slam quarter-finals until his run at Flushing Meadows last year.
"I think I kind of reinvented myself," said the world number 20. "I would say I always believe in myself but there were always ups and downs.
"Sometimes when you have those great results, it shows you what you are capable of. Then you start to believe more and more. This belief and self-confidence appear much stronger after the US Open.
"I made a few semi-finals already, so I hope to continue that way and to grow as a person and as a sportsman."
Khachanov will now meet Stefanos Tsitsipas in the last four after the latter maintained his unbeaten record in grand slam quarter-finals with victory over Jiri Lehecka.
The third seed made it six from six in the last eight at majors with a 6-3 7-6 (7-2) 6-4 victory over 21-year-old Lehecka, who had never won a grand slam match before arriving in Australia.
The young Czech had defeated Cameron Norrie and Felix Auger-Aliassime to make the last eight but was broken in his first service game and, although he put on a creditable display, it was not enough to take a set from Tsitsipas.
The Greek, who along with Novak Djokovic still has a chance of finishing the tournament as the world number one.
