British number one Jack Draper ran out of steam as Spanish third seed Carlos Alcaraz moved into the Australian Open quarter-finals.
Draper, seeded 15th, retired when he was trailing 7-5 6-1 against four-time major champion Alcaraz on a hot day in Melbourne.
The 23-year-old left-hander needed treatment off the court after the first set before abandoning the match at the end of the second.
He held both hands up to the crowd by way of an apology before going off Rod Laver Arena to a warm ovation.
"It is not the way which I want to win," said Alcaraz.