Marion Bartoli overpowered Japan's Ai Sugiyama 6-3, 6-3 to move into the final of the Stanford Classic on Saturday.
The sixth-seeded Frenchwoman will meet Canada's Aleksandra Wozniak, who advanced when top seed Serena Williams was forced to retire with a knee injury down 6-2, 3-1.
In reaching her first final since Wimbledon 2007, Bartoli used a strong inside the baseline attack to repel the 33-year-old Sugiyama.
"I played really well, but she gave me a hard time," said the 15th ranked Bartoli, who was 0-5 against Sugiyama entering the match.
"The last time I played her I wasn't at the same level. I wasn't moving as fast, not serving the same way, I was making more unforced errors and not hitting as hard. Everything is improved now."
Bartoli served well in tight spots, tore at her opponents second serves and mixed it up just enough off the ground to confuse her foe.
She broke Sugiyama to 2-1 in the second set with a backhand down the line winner and never looked back, fighting off a break point at 5-3 and breaking Sugiyama to win on her third match point when the Japanese erred on a forehand.
"I kept my composure and came back with some great serves when I needed to. I've improved my serve in the big occasions," added Bartoli.
Wimbledon finalist Williams took a medical timeout to receive treatment when she was down 5-2 in the first set, but it made no difference. She was unable to put her weight on her left leg and finally gave up.
A disappointed Williams said: "I expected to win this tournament and have a strong start [to the hard court season].
"My goal was to win here and I think I would have done it otherwise.
"I've been playing a lot of tennis so I think that's what it is. When you have inflammation in a joint it's hard to move. Wozniak kept moving me and I was hoping she wouldn't."
Wozniak will play in her first Tier II final on Sunday and is the first qualifier to reach the final stage at Stanford since the WTA computer rankings began in 1982.
"It's my biggest final and I'm really happy the way I've been playing. Coming up from the qualifying its not easy because it's a lot of matches," the 85th-ranked Wozniak said.
Williams was unsure whether she would be able to compete in next week's Los Angles Classic, but said being fit for the Beijing Olympic Games was her top priority.