Defending champion Ana Ivanovic beat Argentina's Gisela Dulko 6-3, 6-3 to reach the fourth round of the WTA event in Indian Wells on Monday.
The Serbian fifth seed was not totally convincing but did enough to set up a clash with Italian 12th seed Flavia Pennetta.
"When it was very close on both sets I stepped up a little bit more and I just went for my shots and followed my instincts. I played really well," Ivanovic told reporters.
With Ivanovic making too many errors early on, 31st seed Dulko broke to lead 3-2 in the opening set.
Ivanovic quickly pulled her game together, however, reeling off four straight games for the set before easing through the second to clinch victory.
Since winning the French Open last summer, Ivanovic has been struggling for confidence, winning just one tournament, at the end of last year.
But the 21-year-old said her new coach, Craig Kardon, who signed up with her last month, has helped restore her belief in her ability.
"I had lots of doubts about my game in the past six months," Ivanovic said. "So finally I feel like I have strategy and also a plan in place again. It gives me a lot of security and confidence."
Pennetta beat American qualifier Angela Haynes 4-6, 6-4, 6-1 while seventh seed Agnieszka Radwanska of Poland and Hungary's 22nd seed Agnes Szavay also advanced to the last 16.