BEIJING - Serena Williams was upset in the second round of the China Open on Wednesday, losing to unheralded Sun Tiantian 6-2, 7-6 (7).

Sun, ranked 127th in the world and fourth among Chinese players, took advantage of numerous¹ errors by Williams, who said she was bothered by an ailing² left knee.

"I just played terrible," Williams said. "Sun played very well and was ready for the match. I'm disappointed³ I couldn't perform better today."

Williams, No. 9 in the world rankings, won last year's event and is very popular in China. However, the crowd cheered as Sun pulled off a surprise victory⁴ — the first of her career against a player ranked in the top 40

北京时间9月21日晚，雅典奥运会女双冠军、中国选手孙甜甜在中网女单第二轮比赛中，6-2/7-6(7)爆冷击败卫冕冠军、种子选手小威廉姆斯，晋级中网女单八强。