Karolina Pliskova advanced to her fifth final of the year, beating American Varvara Lepchenko 6-2 7-5 in the Bank of the West Classic.
The fourth-seeded Pliskova, from the Czech Republic, recorded her 39th victory of the season, one shy of leader Serena Williams. Pliskova will make her top-10 debut when the rankings are released Monday.
“This is the best match I’ve played here so far,” Pliskova said.
“I can still play better. I can change a few things. But I have found some level where I can play. I’ve improved a lot mentally, and I’m going for every shot.”
In her previous four finals appearances this year, Pliskova won in Prague and lost in Sydney, Dubai and Birmingham, England.
Lepchenko, who knocked off top seed Carolina Wozniacki in the second round, committed 50 errors, 24 of them unforced.
Fifth-seeded Angelique Kerber of Germany advanced to the final with a 6-3 6-1 victory over Elina Svitolina of Ukraine in a match that lasted 55 minutes.
“She’s tough to play because she is everywhere and is hitting fast,” Pliskova said.
“She’s a lefty, which also makes it tough. I’ve beaten her a few times and she’s beaten me a few times.”