Indian Wells, California  - Defending champion Ana Ivanovic secured free passage into the semi-finals of the Indian Wells Masters on Thursday when opponent Sybille Bammer withdrew with a left shoulder injury.

The walkover puts the fifth-seeded Serb into a semi-final against breakthrough Russian teenager Anastasia Pavlyuchenkova, who knocked out Polish seventh seed Agnieszwa Radwanska 7-6 (10-8), 6-4.

"I'm very disappointed that I am not able to play," said the Austrian Bammer.

"I normally play very well here and it is a place I really enjoy. I was playing better and better every round, and had a good feeling about today's match.

"Unfortunately, my shoulder injury is making it impossible for me to play. I hope that the injury heals quickly and that I am able to return to action soon."

Pavlyuchenkova, ranked 42nd, was playing in her third quarter-final of the season after Sydney and Paris and has never advanced this far at the WTA level.

"I'm very excited now, and more and more every day because I keep winning," said the Russian who beat second seed Jelena Jankovic in the second round last week.

"It's really big achievement for me this week. I beat some really good players.

"I'm very happy, especially today. It's my first time in semis. I've played Agnieszka five or six times already. She's a very tough player for me. I'm very happy I went through," said Pavlyuchenkova. dpa