Caroline Wozniacki's 20-match winning streak in New Haven ended Friday when the four-time defending champion retired from her semifinal match with Maria Kirilenko with a knee injury.
Wozniacki, who injured the right knee in her quarterfinal win Thursday, called for the trainer right after dropping the first set of the semifinal 7-5 to the 25-year-old Russian.
''I could feel it from the start,'' she said. ''But, you know, it just started to get a bit worse. I decided to stop because if you don't feel a hundred percent, you can't compete at a hundred percent. It's better to let it rest. I wasn't going to win this match anyways if I'm not on a hundred percent fit level.''
The third-seeded Dane had won all 20 matches she played at the tournament since entering as a relatively unknown 18-year-old in 2008. She hadn't dropped a set here since the 2010 final.
Wozniacki was trying to join Martina Navratilova, Steffi Graf and Chris Evert as the only players to win five consecutive champio...