STANFORD, Calif. -- Olga Govortsova, ranked 83rd in the world, ended a frustrating run of results with a convincing 6-2, 6-4 victory over No. 2 seed Samantha Stosur in the second round at the Bank of the West Classic on Tuesday.
Govortsova won back-to-back matches for the first time this season. She had lost seven of her previous eight entering the tournament.
"It helped that I had the extra match and I played four matches in World Team Tennis last weekend," Govortsova said. "I don't think she has played since Wimbledon."
The 25-year-old Belarussian beat Germany's Julia Goerges in straight sets in the first round.
Govortsova earned her ninth win over a top-20 opponent and her first since beating Agnieszka Radwanska via retirement at New Haven last year. This is also the first time she has reached a quarterfinal round this season.
Stosur, ranked 13th, reached the third round at Wimbledon. The Australian was knocked out in the first round for the first time since early May -- a span of five tournaments.
"She was playing quite well and I wasn't able to combat what she was able to do," Stosur said. "Things were slowly turning around, and I had a break to go 5-5. I gave myself a chance to get back into the match but I had to win that last game."
Stosur had 10 double faults, including two in a row at one point.
"That didn't set a good tone for the match," she said. "It is inexcusable to get that many in one match."
Seventh-seeded Urszula Radwanska downed American Christina McHale, 6-1, 6-3 while Daniela Hantuchova beat Yanina Wickmayer 6-2, 4-6, 6-0, in their first-round match.
"I've played for a long time but not for myself until now," Hantuchova said. "I'm very relaxed, playing for myself and enjoying the pressure. I can see the results on the court."
In other matches, sixth-seeded American Varvana Lepchenko beat qualifier Michelle Larcher de Brito of Portugal 6-2, 6-4; qualifier Coco Vandeweghe, a finalist last year, downed Romania's Monica Niculescu 6-0, 6-3; Austria's Tamira Paszek was ahead 6-1, 6-7(4), 3-0 and advanced when Russian qualifier Alla Kudryavtseva retired ; and Russian qualifier Vera Dushevina topped New Zealand's Marina Erakovic 6-2, 6-1