France's Marion Bartoli upset American Venus Williams 6-2, 5-7, 6-4 to win the Stanford Classic on Sunday.
World number 14 Bartoli dominated the back court rallies, served and returned with aggression and shook off a case of nerves that cost her the second set.
Eighth seed Bartoli served for the match at 5-4 in the second set, but played passively and was broken by twice Stanford champion Williams, who then won the set when Bartoli double faulted.
"I was just getting tighter and tighter and Venus felt it right away and she came up with some great winners," Bartoli said.
But the Frenchwoman, thrashed by the American in the 2007 Wimbledon final, kept charging and after breaking Williams to 4-3 in the third set, held her nerve.
She fell behind 0-30 in the final game, but then nailed four straight winners, including a big serve to win the contest.
"I said to myself the only chance to win is to take charge because Venus is not going to give it to you so you have to come up with some winners," Bartoli said.
"It was the best effort I ever gave on court."
Looking to win her first U.S. outdoor hard court title since 2002, the second seeded Williams showed little of the form that produced convincing earlier wins over Maria Sharapova and Elena Dementieva.
"Marion played really well," said Williams, who committed 59 unforced errors to 23 from Bartoli.
"I just couldn't find my game. I was fighting a lot against myself and her. I couldn't find the court.
Ultimately I just ran out of time."
The Stanford title was Bartoli's fifth crown overall, but the first time the 24-year-old has won a WTA Premier level event.