BEIJING - World No 12 Agnieszka Radwanska booked a berth of the semifinal due to the injury retirement of Serbian former world No 1 Ana Ivanovic at China Open here on Friday.

Ana Ivanovic of Serbia returns the ball to Agnieszka Radwanska of Poland during their quarter-final match in the China Open tennis tournament at the National Tennis Center in Beijing October 7, 2011. [Photo/Agencies]

It was Ivanovic's third appearance at China Open. She reached the quarterfinals in 2008 and 2010, but failed to make it to the semis in both occasions. She also retired from the Beijing Olympics three years ago on the same court.

"I love coming here and competing,"  said Ivanovic. "It was very tough to pull out of Olympics, and it's very tough today."

Ivanovic had been struggling with her back since the beginning of last week in Tokyo.

"I have been doing lots of treatments on it, but it hasn't been really getting much better," said Ivanovic.

The 23-year-old Serb delivered strong forehand strokes and got herself a break point in the very first game. Radawanska, who got her sixth and most precious personal WTA title in Tokyo earlier this month, resisted the challenge from Ivanovic by claiming the first game with accurate backhand rallies.

Radwanska found her own chance in the third game, and she converted her second break point to get a 2-1 lead. The 22-year-old Pole refused to give Ivanovic any more opportunity, winning the first set 6-3.

Ivanovic called two medical time out before and during the second set. She decided to retire from the match after losing three straight games in the second set. Her withdrawal promoted Radwanska one step closer to the WTA finals, which was to be held in Istanbul, Turkey.

"Next year I think it's going to be a big year for me, and I really feel it's my opportunity to try and aim for the top again and maybe win a Grand Slam," said Ivanovic.