American teenager Sloane Stephens upset No. 7 seed Julia Goerges 6-3, 7-5 despite a potentially costly and embarrassing mistake in a second-round match Wednesday in the Mercury Insurance Open.

Stephens, 18, beat her German opponent with a steady ground game and won despite squandering a set point when she allowed an out ball to hit her in the back.

Stephens was ranked No. 131 in the world. Goerges was ranked 20th.

"I knew definitely she is an awesome player," Stephens said. "But today wasn't her best day. I'm happy I got her on this day. But everyone has their days and today wasn't hers. I guess it was mine."

No. 11 seed Maria Kirilenko of Russia withdrew from the tournament Wednesday with a left hip injury before her second-round match against Romania's Tamira Paszek. Stephens will face Paszek in the quarterfinals.

Sabine Lisicki, the No. 12 seed from Germany, overwhelmed 40-year-old Kimiko Date-Krumm of Japan 6-1, 6-2 in a second-round night match.

Lisicki moved into the quarterfinals where she will face local favorite, 19-year-old Coco Vandeweghe, a 6-7 (5), 6-4, 6-3 winner of lucky loser Olga Savchuk of the Ukraine.

Fifth-seeded and former world No. 1 Ana Ivanovic of Serbia was a 6-1, 7-6 (5) winner over Japan's Ayumi Morita. After winning the first set easily, Ivanovic lost the first five games of the second set before rallying to win five consecutive games and force the tiebreaker.

No. 4 seed Peng Shuai of China, who had a first-round bye, advanced to the quarters with a 6-1, 6-3 win over Anastasia Rodionova of Australia. Eighth-seeded Daniela Hantuchova of Slovakia also won her first match 6-1, 6-3 over Barbara Zahlavova Strycova of the Czech Republic.

Zheng Jie of China upset No. 9 seed Roberta Vinci of Italy, 6-4, 6-2, and No. 16 seed Polona Hercog of Slovenia lost 4-6, 6-1, 6-4 to Russia's Vera Dushevina.

Stephens registered consecutive victories in a Premier WTA event for the first time in her career. The highest-ranked player Stephens had previously defeated was then-No. 67 Lucie Hradecka of the Czech Republic last season at Indian Wells.

The win allowed her to laugh at the set point she gave away when Goerges hit a ball long, but Stephens inexplicably allowed the ball to hit her in the back. Goerges called it "the funny point."

"That was so embarrassing. I don't know what happened," Stephen said. "I was watching it, I tried to get out of the way. ... That's never really ever happened to me before. It was embarrassing, it was funny, it was childish, something an 18-year-old would do."

Goerges, who has two wins this season over top-ranked Caroline Wozniacki, is struggling on the hardcourts after losing last week in the first round of the Bank of the West Classic at Stanford.

"If you saw me play last week, it's not so frustrating," Goerges said. "It's been a big improvement. I am trying to play my game and I am going for it the whole match. Obviously, it is not working out right now, but it's the right way to come back."

Morita knocked out Ivanovic in the first round at Stanford in straight sets.

"I think this was a whole different match," Ivanovic said. "It was a whole higher level than last week. I can see lots of improvement."