Li Na of China returns the ball during the women's singles third round match against Laura Robson of Britain at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)

Laura Robson of Britain returns the ball during the women's singles third round match against Li Na of China at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)

Li Na of China returns the ball during the women's singles third round match against Laura Robson of Britain at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)

Li Na of China returns the ball during the women's singles third round match against Laura Robson of Britain at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)

Laura Robson of Britain returns the ball during the women's singles third round match against Li Na of China at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)

Laura Robson of Britain returns the ball during the women's singles third round match against Li Na of China at the U.S. Open tennis tournament in New York, the United States, Aug. 31, 2012. Li lost the match 1-2. (Xinhua/Wang Lei)