Kerber, Wozniacki advance to semis via walkover at Indian Wells

Both Angelique Kerber and Caroline Wozniacki advanced to the semifinals of the BNP Paribas Open after their quarterfinal opponents were forced to withdraw because of injury.

Top seed and defending champion Victoria Azarenka was scheduled to play Wozniacki, but couldn't battle through a right ankle injury and was unable to go. She had not lost a match this year since pulling out of Brisbane with a toe injury.

"On my warmup today I tested it out as much as possible," Azarenka said in a press conference Thursday afternoon. "I tried absolutely everything I could to do, but I have been advised by the doctor, by my own team, that it's just a very, very high risk already. I mean, it's already really painful, but it's very high risk to make it much worse."

Kerber's opponent, Sam Stosur, also was forced to withdraw because of a right calf injury, which she injured in her fourth-round win over Mona Barthel.

"I hurt my right calf muscle in the last game of my match against Mona Barthel when I was serving for the match, so I don't know if you can get any more unlucky than that," Stosur said Thursday morning.

"It's really disappointing. I love the conditions here at the BNP Paribas Open and I love playing in front of this crowd, so to have to pull out without even being able to get on court is probably as bad as it gets. I think this is only the second time I've ever pulled out of a match in my career, and unfortunately there isn't anything I can do about it."

The fourth-seeded Kerber will now challenge former world No. 1 Wozniacki in semifinal play.

Kerber will play in her second semifinal of 2013 -- having lost to Dominika Cibulkova in the Sydney semis back in January -- while Wozniacki will appear in her first. Wozniacki won this event back in 2011.

Maria Sharapova and Maria Kirilenko have already advanced to the final four, winning quarterfinal matches on Wednesday. Sharapova, the 2006 Indian Wells champ and last year's runner-up to Azarenka, topped Sara Errani in straight sets, while Kirilenko dumped fifth-seeded Czech Petra Kvitova in three.

This Premier Mandatory WTA event will pay its newest champion $1 million.