Maria Sharapova overcame a fast-starting Agnieszka Radwanska1-6, 6-2, 6-2 to reach the final of the Stanford Classic on Saturday.
Bidding for her first WTA Premier title of the year, Sharapova needed five match points to subdue third seed Radwanska, who engaged the hard-hitting Russian in one long rally after another.
Sharapova will face Belarussian Victoria Azarenka in the final, who celebrated her 21st birthday in style earlier by overwhelming top seed Samantha Stosur 6-2, 6-3.
Coming into the tournament, the fifth seeded Sharapova had not beaten a top 25 player all season, but at Stanford has now taken down number 23 Zheng Jie of China, number six Elena Dementieva of Russia and number 11 Radwanska.
The three-time grand slam champion was finally able to repel the Pole's challenge when she boomed a service winner.
"This week has been great for me, going against different types of games, finding myself in different situations and coming out with wins," Sharapova said. "But there's another one tomorrow and I have finish it out."
The eighth seed Azarenka registered her fourth victory over the Australian in as many attempts, tearing apart Stosur's second serves and battering her from inside the baseline.
Azarenka broke World N o 5 Stosur five times in the match and was a broken only once herself.
"I was very good on the return, putting pressure on her," said Azarenka, who reached her third final of the year. "I was very solid from the baseline and I was able to keep holding."
Former world number six Azarenka, who has battled with leg injuries for much of this year and saw her ranking dip to 18, said she was now healthy.
Stosur's big serve consistently let her down and she was only able to land 55 percent of her first serves. She was also constantly pushed around the court in rallies and committed 33 unforced errors to only 15 from her opponent.
"She played quite well and punished me when I didn't put a good serve in," Stosur said. "It wasn't my best day and I still had quite a few chances to get back in it, but when I had those I didn't come up with the goods."
Azarenka has three career titles and this year reached the finals in Dubai and Eastbourne but she has not won in 16 months since crushing Serena Williams in the 2009 Miami final.
Stosur is the first top five player Azarenka has beaten since she overcame Williams, who is now World No 1.
"Sam is great player and has had amazing results this year," Azarenka said. "I'm very happy that I could beat her when she's in good form. It gives me confidence."