Second seed Maria Sharapova and Swiss comeback queen Martina Hingis advanced in straight sets, both reaching to the third round of a 1.34 million-dollar WTA hardcourt event.
Sharapova, playing her first match since Wimbledon, defeated fellow Russian Vasilisa Bardina 6-4, 6-1 while Hingis beat Meilen Tu 6-2, 6-3 in her first Southern California match since 2001.
"I'm excited going into a tournament feeling healthy and playing pretty well," Sharapova said. "It's a matter of getting into the matches again. I'm happy to win the first round, but there's a long way to go."
Beating Bardina was just the first step Sharapova expected.
"I felt good. We had some long rallies at the start," she said. "But after she broke me in the first set, I made her play a bit and put pressure on her. I felt really good out there."
Five-time Grand Slam winner Hingis, who came back to the sport after a three-year absence, advanced after a first-round bye in 66 minutes over the 91st-ranked American.
Hingis turned back the clock and improved to 15-3 at the tournament. She staved off six break points while breaking three times in the comfortable victory.
In their junior days, Tu beat Hingis in the final of the 2004 US Open juniors, a match which Hingis certainly recalls. But her game has moved on in the past dozen years.
"When they were reading my accomplishments in the (pre-match) warmup, it sounded like a fairytale," said 13th-ranked Hingis.
Hingis next plays either Italy's Flavia Pennetta or American Jamea Jackson.
The eighth-seeded Swiss won the tournament on her debut as a teenager during the magical 1997 season in which she lifted three of the four majors.
Her last appearance was a semi-final run five years ago against Monica Seles.
"The fun is back - but only when you win," said Hingis. "I've worked hard for the last two weeks.
"But your recovery time is not the same as when you are 17. I used to get back onto the court after an hour or two hours of rest. Now, I take three or four."
"I wasn't that tired today but my game will come around even more after a few more matches. I have to work more on conditioning, train in a different way now."
Hingis, 25, cemented her return to the game with the Rome title in May, but is starting afresh in San Diego in hopes of erasing memories of a third-round Wimbledon upset loss to Japan's Ai Sugiyama.
Sugiyama, last year's finalist here, suffered a surprise loss earlier as she went out in the first round to Russian Vera Zvonareva 6-1, 7-5.
A pair of Croatians crashed out, with Alona Bondarenko of Ukraine ousting Ivana Lisjak 6-2, 7-6 (7-2) and Russian Anna Chakvetadze defeating Jelena Kostanic 6-4, 6-3.
The US Open tune-up's field is headed by Belgian Kim Clijsters, who began her summer with a hardcourt title at the weekend at Stanford.