STANFORD, Calif. (AP) Sixth-seeded Andrea Petkovic got her body realigned and returned to form to beat fellow German Carina Witthoeft in a first-round match of 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.''
The seventh-seeded Madison Keys also advanced. The 18th-ranked American needed just 5 minutes to take care of Aleksandra Krunic 6-3, 6-0.
''I think I played really well,'' Keys said. ''Once I got the lead I tried to keep the pressure on her. My first serve was definitely working for me and that's something I want to keep up.''
American teenager CiCi Bellis lost her match to qualifier Misaki Doi, 6-3, 7-6 (3). Bellis was the youngest player in 15 years to win a match at the U.S. 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 U.S. Open at the end of the month. Doi meets No. 2-seed Agnieszka Radwanska on Thursday. Mona Barthel beat wild card Carol Zhao 6-3, 6-0.
World No. 1 and defending champion Serena Williams withdrew last week due to injury.