British number one Heather Watson was knocked out of the WTA Mercury Insurance Open on Wednesday, going down in straight sets to world number 161 Chan Yung-Jan.
The 20-year-old, ranked 71 in the world, lost her first service game and the 22-year-old from Chinese Taipei never looked back as she triumphed 6-3 7-6 (7/2) in their second-round clash in Carlsbad, California.
Watson, who claimed the first WTA title of her career on Sunday in the doubles competition at the Bank of the West Classic, will remain in California for the doubles before returning to Britain to compete at the London Olympics.
Meanwhile, top seed Marion Bartoli progressed to the quarter-finals on Wednesday but had things far from all her own way against American Vania King.
The world number 10 from France was playing her first match in Carlsbad, after receiving a first-round bye, and had to work hard to overcome her American opponent 6-4 5-7 6-4 in the second round.
Fourth seed Nadia Petrova made smooth progress with a 6-4 6-3 victory over American Alexa Glatch. She will face Varvara Lepchenko in the last eight.
Lepchenko, a member of the United States team for the London Olympics, stunned eighth-seeded South African Chanelle Scheepers 6-4 6-2.