Madison Keys won just two matches but made a big impression at Wimbledon and the American teenager carried on where she left off in London by stopping a seed in Stanford.
Keys, 18, knocked out British hope Heather Watson and Germany's Mona Barthel on her senior Wimbledon debut, before taking a set off world number four Agnieszka Radwanska in the third round.
The world number 44 proved too strong for Slovakian eighth seed Magdalena Rybarikova on the opening day of the Bank of the West Classic, winning 6-2 6-2.
Romanian fifth seed Sorana Cirstea avoided a slip-up, also winning 6-2 6-2, with Japan's Ayumi Morita her victim.
Former top-20 player Julia Goerges continues to slide. Ranked 18th at the end of last season, the 24-year-old German has tumbled to 43rd and a 7-6 (7/2) 6-2 loss to Olga Govortsova of Belarus was her latest setback.
Former French Open champion Francesca Schiavone and Swiss Stefanie Voegele both successfully came through the first round.
Serena Williams has won the Stanford title in each of the last two years but is missing the event this year, with Radwanska the top seed.