The Mexican star, an eight-time winner in 2007, is 16 under and leads Paula Creamer and Annika Sorenstam, with Karrie Webb a stroke further back.
"It was a tough day today, it started in the morning with some rain and I didn't feel as good a rhythm as I had the first few days so it was difficult for me out there," Ochoa said.
Creamer shot a 2-under 70 to finish 8 under along with Sorenstam, who made five birdies but conceded a bogey and a double bogey.
"I was kind of disappointed to lose a shot or two shots back there, particularly when I made a good start and made the turn at 3-under. You kind of like to continue the momentum," said Sorenstam. "But I bounced back and there were some good shots and good golf."
Webb had four birdies and two bogeys for fourth place. Laura Diaz of the United States was 5-under after a 2-under 70 round that included four birdies and two bogeys.
Creamer and Sorenstam are the LPGA Tour's first two winners this season. The American won the Fields Open last weekend and Sorenstam is the SBS Open champion.
Shin Ji-yai (70) and Kim In-kyung (74) of South Korea and Stacy Prammanasudh (73) of the United States were tied for sixth place at 4-under.
Americans Morgan Pressel (73), Pat Hurst (73) and Angela Stanford (72), and Birdie Kim of South Korea (71) were 2 under.
Laura Diaz was 5-under after a 2-under 70 that included four birdies and two bogeys.
