Tim Henman reached the US Open quarter-finals for the first time after German Nicolas Kiefer retired with injury.
Henman battled back from a poor start and had victory in his sights with the match poised at 6-7 6-3 6-1 6-7 3-0 before Kiefer damaged a tendon.
The German complained he felt no power in his right wrist after a serve.
Henman, celebrating his 30th birthday, will now face Slovakia's Dominik Hrbaty on Wednesday for a place in the last four at Flushing Meadows.
"It's a strange way to win a match after I'd been fighting so hard," admitted Henman.
"But I thought I'll take it after we'd been playing the way we had.
"Kiefer told me he felt something pop in his wrist and it was a tough break for him."
The German 27-year-old will now have further tests to determine the extent of his injury.
"I hit a reflex volley and when I tried to hit a big serve on the next point I couldn't hold the racket," said Kiefer.
"It was a tough decision because I wanted to finish the match."
Henman's own progress at Flushing Meadows was almost undone by a back injury but he has shown great determination to pull off his best-ever US Open performance.
The fifth seed is now the firm favourite for his quarter-final tie and Henman is cautiously optimistic.
"It's funny how things have changed," said Henman. "I've played some good tennis and that gives me confidence going into the latter stages.
"It seems when I release the pressure on myself - and it took a back injury to do it - then I play my best tennis.
"Everything so far has been a bonus and this is a good way to finish my birthday."
The match on Arthur Ashe Court had swung back and forth in favour of both players.
Henman found himself 4-0 down in the opening set as his serve deserted him.
And despite recovering to break Kiefer twice and saving a set-point, he could not prevent the in-form German wrapping up the tie-break 7-5.
Kiefer looked to be in control as he grabbed a break to go 3-1 up in the second set.
But a dogged Henman notched up 10 straight games to take the next two sets with ease.
The fourth set was an intense encounter and Kiefer let his anger get the better of him as he bitterly disputed a foot-fault and a line-call.
However, the German was able to keep a cool head to edge the tie-break 7-5 with some searing backhands and force a fifth set.
It was Henman who shook off a shaky start to race to a 3-0 lead in the decider.
But the crowd were denied a thrilling finale as Kiefer decided to retire after a lengthy consultation with his trainer.