The Mexican, a three-time winner on the LPGA Tour, stands at 9-under-par 207 after 54 holes. She has led three other LPGA events in her career after 54 holes and has won one of those three. She finished second the other two times.
Teenage star Michelle Wie hung on to second place with a 1-over 73. She stands at 6-under-par 210 and is also in search of her first major title, as well as her first win on the LPGA Tour.
Natalie Gulbis (68), Shi Hyun Ahn (71) and Seon-Hwa Lee (74) share third place at 4-under-par 212. A pair of former winners here -- Helen Alfredsson and Karrie Webb -- are tied for sixth place at minus-2 on the Dinah Shore Course at Mission Hills Country Club.
Annika Sorenstam, the defending champion and three-time winner here, still has not gotten anything going this week. She stands at even-par 216 after a third- round, 1-over 73.
Ochoa faltered to a bogey on the first. She came right back with a birdie on No. 2 as she got up and down from a greenside bunker. A three-putt bogey on the fifth dropped the Mexican to minus-10.
The 24-year-old missed the eighth green en route to her third bogey of the round. Ochoa bounced right back with a birdie on the ninth when she made a 14-foot putt to turn at 10 under.
Ochoa, who set a new course record on Thursday with her 62, parred the first four holes of the back nine. She missed the green long on the 14th, then ran her chip 20 feet by the cup. Ochoa two-putted for bogey to slip to minus-nine. She parred out to take a three-shot lead into the final round.
'It was a tough day today out there. I guess, the third round, I had a lot of pressure and adrenaline playing in the last group with Michelle, that was exciting,' Ochoa said. 'I'm happy the way I finished.
'I still have a three-shot lead, and this course was very hard in the afternoon. It was good for me. It was a good round. I feel like I'm hitting the ball really good. I'm happy with the finish, and I can't wait to be here tomorrow.'
Wie slipped to a bogey of her own on the third to fall to minus-6. Other than that, she parred 11 of the first 12 holes.
The young Hawaiian dropped another stroke on the 13th, but quickly atoned for that error with a 15-foot birdie putt on the 14th. Wie closed with four straight pars to remain in second.
'My game felt very solid today. It was a bad break kind of day for me,' Wie said. 'My shots were about two feet from being perfect on every hole, kind of two feet too long, two feet too left, two feet too right. My game still feels very solid right now and I'm ready for tomorrow.'
Sorenstam looked to finally be making her move early on Saturday. She opened with birdies on two and three to get to 3 under for the tournament.
The women's world No. 1 bogeyed the fifth, but got that stroke right back with a birdie at six. Sorenstam turned at minus-2 after a bogey on the eighth. She played the back nine in plus-2 to end nine back of Ochoa.
Hee-Won Han tied Gulbis for the low round today with a 4-under 68. That moved Han into a tie for eighth at 1-under-par 215 with 2004 Women's British Open champion Karen Stupples and rookie Morgan Pressel.
Sorenstam was joined at even-par 216 by Michele Redman, amateur Angela Park, Stacy Prammanasudh, 1983 runner-up Beth Daniel, two-time winner Juli Inkster and Brittany Lang.