US teenager Sloane Stephens shocked seventh-seeded German Julia Goerges 6-3, 7-5 on Wednesday at the WTA San Diego Open to earn her first career victory over a Top 20 player.
Stephens, ranked 131, ambushed the 20th-ranked Goerges, who won the Stuttgart title on clay and beat number one Caroline Wozniacki twice in the first half of the season.
Stephens was 0-3 against the Top 20 before beating Goerges.
Russian Vera Dushevina ousted another seed at La Costa, defeating number 16 Slovenian Polona Hercog 4-6, 6-1, 6-4 in the second round.
Austrian Tamira Paszek did the same but without firing a shot as number 11 Russian Maria Kirilenko withdrew before their second-round match due to a left hip injury.
Pasek and Stephens now face off in a battle of young guns for a quarter-final spot.
France's Virginie Razzano, a quarter-finalist last week in Maryland, continued her good hardcourt form by taking out New Zealand's Marina Erakovic 6-1, 6-3.
Stephens, 18, won back-to-back matches for the first time in her career at the WTA level after beating China's Zhang Shuai in the first round.
The American said she was frankly surprised to have advanced over Goerges.
"I had nothing to lose but I wasn't expecting a win," Stephens said.
"She played well with a few mistakes," Stephens added of Goerges, who has now lost all three of her post-Wimbledon matches. "She's still an awesome player, she's not just any girl.
"She didn't have her greatest day and maybe I did. I'm happy to take this victory."
Goerges said that her season's goal is to improve her consistency.
"I've been down and up and now maybe a bit down. There are a lot of good young players out there," said the 23-year-old. "I need to stay consistently at my level.
"I'm going back to the practice courts."
Goerges was one of a trio of fast-rising Germans making their San Diego debuts.
Second seed Andrea Petkovic is already into the third round after a bye and victory while number 12 Sabine Lisicki will play a second-round match against 40-year-old Japanese Kimiko Date-Krumm, winner of the title a decade and a half ago.