Ochoa, the top-ranked Mexican star who also won the 2006 tournament at Tres Marias, had a 20-under 199 total. After opening with consecutive bogey-free 65s, she had eight birdies, two bogeys and a double bogey Saturday.
The fifth-ranked Pettersen followed her second-round 64 with a 67. She eagled the par-5 eighth and had four birdies, but failed to convert a short birdie chance on 18.
Whatever happened, happened, theres nothing you can do about it. Im happy because there are still 18 holes to play, Pettersen said. It was a good round, not perfect. I managed to gain ground on Lorena, which was one of my goals. Hopefully tomorrow, I can go out and shoot as low as I can.
Na Yeon Choi (69) was third at 15 under, Wendy Ward (66), Morgan Pressel (67) and Irene Cho (68) were 14 under, and Cristie Kerr (66) and second-ranked Yani Tseng (66) were another stroke back.
Michelle Wie was tied for 13th at 10 under. She shot a 72 after opening with rounds of 66 and 71.