British number two Cameron Norrie has reached the semi-final of the Atlanta Open after Nick Kyrgios retired midway through their quarter-final match.
Norrie, the world number 73, took the first set 7-5, serving up two aces, as Australian Kyrgios began showing signs of a recurring hip injury.
After seeing the trainer in the first set, Kyrgios then went 3-0 down to the 22-year-old Briton in the second before deciding to pull out of the match, prompting a chorus of boos from the crowd.
Norrie, advancing to his second ATP World Tour semi-final after making the same stage at the Lyon Open in May, admitted it was not how he had hoped to reach the last four, where he will meet American Ryan Harrison.
"It feels great to get into the semis, but not the way I wanted to do it today," Norrie told the ATP's official website.
"I have played really, really well all week. I am looking forward to my match tomorrow against Harrison. It is going to be a battle. We have both played good tennis all week."
Harrison earlier defeated Hyeon Chung 6-7 (3/7) 6-2 7-6 (7/5), while John Isner beat Mischa Zverev 7-5 4-6 6-1 in his quarter-final.