Wimbledon 2012: Kim Clijsters reaches 4th round

Kim Clijsters reached the fourth round of Wimbledon on Friday when 12th-seeded Vera Zvonareva retired with an apparent respiratory problem when trailing 6-3, 4-3.

Zvonareva was coughing loudly during the match and the 2010 finalist was in tears as she needed a medical timeout at 2-1 in the second set. The trainer took her pulse and she was examined with a stethoscope before resuming play, but had to retire four games later.

Clijsters said, "I think she was having difficulties breathing" and that it's "sad to see her end the tournament this way."

The Belgian is playing in her last Wimbledon as she plans to retire after this year's U.S. Open. She will next play No. 8 Angelique Kerber, who beat Christina McHale of the United States 6-2, 6-3.