SAN JOSE, Calif. (AP) -- Maria Sakkari of Greece upset third-seeded Venus Williams 6-4, 7-6 (2) on Friday night in the quarterfinals of the Mubadala Silicon Valley Classic.
Sakkari came back from 0-3 in the first set and 3-5 in the second set. She advanced to face American Danielle Collins -- with the winner reaching her first WTA final.
Collins, a two-time NCAA champion for Virginia, advanced after former world No. 1 Victoria Azarenka of Belarus retired midway through the second set due to injury.
Azarenka led 4-2 in the first set before needing a tiebreaker to win the 72-minutes set 7-6 (4). She grabbed her right leg in the opening game of the second set, lost the first three games and was evaluated by a trainer and doctor before retiring prior to the fourth game.
Fifth-seeded Mihaela Buzarnescu of Romania secured the first semifinal spot by beating Australia's Ajla Tomljanovic 6-1, 7-5. The Romanian will face No. 4 seed Elise Mertens.
Mertens, a Belgian, saved two set points in the first set, forced a tiebreak and won four straight games in the second set for a 7-6 (4), 6-3 victory over Johanna Konta. It's Mertens' fifth WTA semifinal of the year.