San Francisco (AFP) - Alison Riske overcame some third-set jitters to beat Varvara Lepchenko 2-6, 6-3, 7-6 (7/4) and advance to the second round at the WTA Tour's Stanford tournament.
Riske had to rally twice in the match against the eighth-seeded Lepchenko, dropping the first set and then letting a 4-2 lead slip away in the third before winning in a tie-breaker.
She jumped out to a 5-2 lead in the tie-breaker before clinching the all-American encounter after two hours and five minutes.
Riske, ranked 78th in the world, improved to 11-12 on the year. She next plays Romanian qualifier Ana Bogdan.
Riske now has a 3-2 edge over Lepchenko in career meetings, having won the last three after dropping the first two matches.
She is trying to improve on her quarter-final showing in her debut in this event last year.
Riske reached the final in her first tournament of 2016 in Shenzhen, where she lost to Agnieszka Radwanska. But she struggled to find her form since, losing in the first round of the Australian Open and at Indian Wells.
In the night session 17-year-old American Catherine Bellis posted her first main draw win of the season outlasting fellow teen Jelena Ostapenko in straight sets 6-4, 6-4.
Bellis, who burst onto the scene in 2014 when she became the youngest at age 15 to win a main draw match at the US Open, benefitted from the sixth seeded Ostapenko's nine double faults.
"In the end, I was just a little bit more consistent than she was," Bellis said. "I had a couple of heart attacks, but it's all good."
In other matches Tuesday, Poland's Magda Linette beat Czech Kristyna Pliskova 2-6, 6-2, 7-5; American wildcard Julia Boserup beat Japan's Naomi Osaka 2-6, 6-4, 6-4 and Urszula Radwanska of Poland toppled Kateryna Bondarenko 6-4, 7-5.
Boserup, who reached the third round of Wimbledon this year in her Grand Slam debut, managed to win Tuesday despite making eight double faults and posting just one ace.
Osaka blasted seven aces and had two double faults in the two hour, nine minute match.
Boserup will square off against third seed Johanna Konta in the second round.