Serena Williams suffered one of the worst defeats of her career as she went down 6-2 7-6 to Sun Tiantian at the China Open in Beijing. The defending champion made a string of unforced errors against the Chinese wildcard, ranked 118 places below her at 127 in the world.
Williams said: "I played terrible. I never expected such a tough match. She played some great shots."
Sun became the second home player to reach the last eight.
China's number one Peng Shuai beat Argentina's Mariana Diaz-Oliva 3-6 6-2 7-6 to reach her fourth WTA quarter-final this year.
Zheng Jie, another Chinese player, upset sixth seed Jelena Jankovic 7-5 4-6 7-5 in a first-round encounter.
Serena's sister, Venus, plays Spain's Nuria Llagostera Vives in her second-round match on Thursday while world number one Maria Sharapova faces Israel's Shahar Peer.
MMIX
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