Stanford - Sixth-seeded Andrea Petkovic got her body realigned and returned to form to beat fellow German Carina Witthoeft in a first round match at the Bank of the West Classic on Monday.
"I played really bad up to 1-5," Petkovic said. "It felt like my upper body and lower body were swapped. After that I played fine."
The 17th-ranked Petkovic won 5-7, 6-1, 6-3.
"Stanford is special with the conditions. The ball really flies," she said. "You have to feel the court."
American teenager CiCi Bellis lost her match to qualifier Misaki Doi, 6-3, 7-6 (7/3). Bellis was the youngest player in 15 years to win a match at the US Open last year.
"I thought I played pretty well and gave her a good fight," said Bellis, who lives a few minutes from the campus. "It's good for me to play against players ranked so high."
Qualifier Nicole Gibbs, who won a pair of NCAA singles titles while at Stanford, beat France's Caroline Garcia 6-4, 7-5, for her first WTA main draw victory since April.
"This was a big barrier for me to break through," Gibbs said. "To do it in front of my home crowd was something special."
American Alison Riske topped German Tatjana Maria 6-2, 5-7, 6-1 to earn a date with third-seeded Carla Suarez Navarro in the second round of the tournament that is a tune up for the US Open in about a month. Doi meets No 2-seed Agnieszka Radwanska on Thursday.
World No 1 and defending champion Serena Williams withdrew last week due to injury.
Results from the first round of the Bank of the West Classic WTA Tournament at Stanford on Monday (x denotes seed):
Andrea Petkovic (GER x6) bt Carina Witthoeft (GER) 5-7, 6-1, 6-3
Alison Riske (USA) bt Tatjana Maria (GER) 6-2, 5-7, 6-1
Misaki Doi (JPN) bt Catherine Bellis (USA) 6-3, 7-6 (7/3)
Nicole Gibbs (USA) bt Caroline Garcia (FRA) 6-4, 7-5
Madison Keys (USA x7) bt Aleksandra Krunic (SRB) 6-3, 6-0
Mona Barthel (GER) bt Carol Zhao (CAN) 6-3, 6-0