Sam Stosur is through to the quarter-finals of the Citi Open in Washington thanks to a Caroline Wozniacki injury.
The second round match between the two WTA Tour veterans was on an even keel with Stosur leading 4-3 in the second set, after Wozniacki took the first 7-5.
Wozniacki retired with an elbow injury.
Stosur will now play 22-year-old American qualifier Jessica Pegula in the quarter-finals after she knocked off fellow American Christina McHale 7-5 6-2 earlier in the day.
"She started kind of running around her backhand a little bit more, which is pretty unusual for Caroline to want to do that. So I kind of thought, 'OK, there's something going on'," Stosur said.
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As for why she had trouble taking control of the match, Stosur replied: "Sometimes it's quite difficult playing somebody who's injured."
The match was played on a secondary grandstand court, instead of in the hard-court tournament's main stadium, which gets more men's matches than women's matches during the joint event.
"I notice there's not too many matches on centre court for the women, unfortunately," Stosur said when asked by a reporter about the scheduling.
"It'd be nice if we were kind of 50-50 on centre court, that's for sure."
The right-handed Wozniacki said that she felt pain while hitting a two-handed backhand at 5-all in the first set of a match that began Wednesday night and ended just past midnight on Thursday.
She was treated by a trainer and wound up winning that set 7-5, but stopped playing after getting broken to trail 4-3 in the second.
"There was a point where I hit a backhand and I just felt it, and I was like 'Oh, it's nothing'," Wozniacki said.
"But then I hit another backhand and I was like, 'OK, it's something.' And it just got worse."
Wozniacki is supposed to represent Denmark at the Rio de Janeiro Olympics next month and carry her country's flag in the opening ceremony.
She won an appeal to the International Tennis Federation to allow her to compete at the Rio Games after she was unable to fulfill the Fed Cup requirements.
