Fifth-seeded Mihaela Buzarnescu will be gunning for her first WTA title on Sunday when she takes on Maria Sakkari in the final at San Jose, California.
Romania's Buzarnescu, ranked 24th in the world, rallied to beat fourth-seeded Belgian Elise Mertens 4-6, 6-3, 6-1.
Mertens, the world number 15, took the first set despite heavy pressure on her serve from Buzarnescu.
The two traded breaks to start the second before the Romanian won four games in a row to take a 4-1 lead.
Heading into the third, Mertens' level had clearly dropped. She called for a trainer to treat her right forearm, but Buzarnescu won the last six games to seal the win and avenge her loss to the Belgian in the final at Hobart in January.
Mertens had gone on to win titles at Rabat and Lugano this year,but was vying to reach the first Premier level final of her career.
Greece's Sakkari, ranked 49th in the world, will also be chasing a first career title on Sunday.
She rallied from a set and two breaks down to beat American Danielle Collins 3-6, 7-5, 6-2.
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