Bartoli gained some revenge for her 2007 Wimbledon final loss
Marion Bartoli of France stunned Venus Williams with a shock 6-2 5-7 6-4 win to clinch the Bank of the West Classic title in Stanford, California.
After failing to serve out at 5-4 up in the second set, the eighth seed recovered her composure to break in the seventh game of the decider.
The 24-year-old went 0-30 down in the final game before four straight winners wrapped up the match.
The title is Bartoli's first win in a top-tier WTA event.
"It was really hard mentally to win the second set because it was getting tighter and tighter," she said. "When I served for the match, she sensed I was tight, and she started coming up with big winners.
Marion played really well today, I have to give her credit for playing so well
"I just tried to stay positive and focused in the third set. We had some great rallies in the third set. It was so hard to win the last game.
"The only chance to win that was to take my chances, because otherwise Venus wouldn't give me anything. I gave everything I had today."
Third seed Williams had reached her 65th career singles final with a 6-0 6-1 demolition of fourth seeded Russian Elena Dementieva.
In contrast, Bartoli had been taken to three sets by Australian Samantha Stosur in the last four.
The pair had previously met in the 2007 Wimbledon final which Venus dominated and won in straight sets.
But pre-match expectations were confounded as Bartoli served and returned with aggression and overcame her second-set nerves to storm ahead again in the third.
"Marion played really well today," said Williams. "I have to give her credit for playing so well. I was fighting myself out there as well as her. It was a tough day.
"I had to fight through it and in the end I ran out of time. My last few matches were so good, but today I just couldn't execute the way I wanted."