Top-ranked Serena Williams won in her first match since defaulting in a doubles match with sister Venus at Wimbledon, beating Karolina Pliskova 7-5, 6-2 on Wednesday night in the second round of the Bank of the West Classic.
At Wimbledon, Williams tried to play through a viral infection that caused her to lose her equilibrium during the doubles match. On Wednesday night, encouraged by a large crowd, Williams fought through a tough first set before she found her legs and took control of the match with a big second set.
"I thought I played well," Williams said. "I'm on the right path, I'm excited and I'm looking forward to my next match."
In the quarterfinals, Williams will meet the winner of Thursday's match between fifth-seeded Ana Ivanovic and qualifier Carol Zhao, a Stanford sophomore playing in her first WTA event.
Earlier, Varvara Lepchenko beat second-seeded Angieszka Radwanska 6-3, 3-6, 6-4 to advance to the quarterfinals.
Lepchenko beat the fifth-ranked Radwanska for the first time in six meetings, edging a top-10 player for only the third time in 24 matches. Radwanska, the runner-up last year, became the highest seeded player to fall in the tournament.
Lepchenko will face Sachia Vickery, the American qualifier who beat Monica Puig 6-7 (4), 6-2, 6-1 to reach her first career WTA Tour quarterfinal. Vickery also won two straight in the main draw for the first time. Her only previous victory came at last year's U.S. Open in her WTA main draw debut.
Also, eighth-seeded Andrea Petkovic beat qualifier Naomi Osaka, 6-2, 6-2. Petkovic will next meet the winner of Thursday night's match between Venus Williams and Victoria Azarenka.