Lindsay Davenport stunned top seed Serena Williams 6-1, 6-3 to capture her fourth JP Morgan Chase Open in Carson, California on Sunday.
The third-seeded American played superbly to win her second title in two weeks by dictating play from the baseline and attacking her erratic opponent's second serve.
Davenport came into the final with a 2-9 career record against Serena and had lost their last four matches.
However, she was the far more consistent player on the day, committing only 12 unforced errors to 29 from Williams.
"I don't know why it all clicked all of a sudden," she said.
"One unforced error from me in the first set is a miracle. I was in control of the points, which I had a difficult time doing against her in the past".
Playing in front of a near sell-out crowd just five miles from where she grew up, Williams never found the game that brought her six Grand Slam titles.
She was blown away in the first set and although she held break points in the last three games of the second set, she never managed to convert on Davenport's serve.
"I feel like the last 10 months I've been building a stronger base physically, can withstand the power and run down some balls," Davenport said. "I have a lot of inner confidence now." Williams has won only title since returning to the tour in March after eight and half months off due to a knee injury.
"I played like a nightmare," Williams said. "I tried to commit suicide out there. I pretty much killed myself. I had an awful, horrendous, terrible, miserable and horrible day."
Three weeks ago, Williams failed to defend her Wimbledon crown against 17-year-old Maria Sharapova. On Sunday, she felt much the same.
"It was the second time I've committed suicide this year," the world number 10 added.
"I've got to stop playing 1,000 feet behind the baseline and move up to the ball. I've got to get serious."
Davenport, who beat Venus Williams in last week's Stanford final, moved up to number four in the rankings with the victory.
"I've had a tough time playing the Williams sisters over the last four years," Davenport said.
"Going out and playing good tennis and being able to withstand two full weeks against good players is great. I'm building and want to keep the momentum going."
The 28-year-old will attempt go for her second "California Triple" next week in Carlsbad.
The last time she managed the feat in 1998, Davenport went on to win the U.S. Open title.
"I have one more to go before I match 1998. The most important thing for me is to stay healthy," said Davenport, who suffered a knee injury at the French Open and is travelling with a trainer and physical therapist.
"Six years ago was a fantastic run and I feel like I am in the same position I was then, but I still have five weeks to go before the U.S. Open."