Caroline Wozniacki

Wozniacki stops match in Washington with injured left arm

Former No. 1 Caroline Wozniacki retired from her second-round match at the Citi Open against Sam Stosur because of an injured left arm.

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...