Ochoa, who tops the money list with $1.25 million, closed with two birdies and enters the final round at 9-under 207.
'It was one of those days that everything is easy -- hitting the driver good and giving myself a lot of birdie chances,' she said. 'Once you're playing good, you just need to be aggressive. ... I make mistakes when I don't play aggressive.'
The 19-year-old Kim, whose best finish was a tie for fourth at last month's Corning Classic, sank a 25-foot birdie putt on No. 17 for a 71. That kept her close heading into Sunday at the tree-lined Locust Hill course.
'If I play my best, I don't think I'm going to have any regrets,' she said. 'I don't think I'm afraid to fail. ... I just feel very calm.'
First-round leader Cristi Kerr rallied with a 70 to move into third place at 5 under, one ahead of Lindsey Wright, Mi Hyun Kim of South Korea, A.J. Eathorne and Angela Stanford.
Stanford, whose sole victory came at the ShopRite LPGA Classic in 2003, briefly took the lead at 9 under but closed with three bogeys and a double-bogey. Defending champion Jeong Jang shot a 71 to get to 1 under.
Ochoa won the Safeway International in March and the Sybase Classic in May, has finished runner-up three times and placed in the top 10 five other times in 2007.
The Mexican picked up the first of her six birdies with a 12-foot putt on No. 2. A wayward drive on No. 6 produced her only bogey. She two-putted for birdie on the par-5 17th and took the outright lead when she left her 125-yard approach shot 2 feet away on the last hole.
'I always play to win,' Ochoa said. 'I know I can win anytime I play. I have the confidence and trust and faith. I have nothing to prove. I enjoy very much what I do and it's fun just to be out there and trying to make birdies.'
'I did everything I could today,' she added. 'I'm very pleased and I can't wait to be here tomorrow.'
Ochoa won here in 2005, rallying from five strokes back with just seven holes to go to beat Paula Creamer by four strokes.
Sandwiched between two majors, the $1.8 million tournament drew 47 of the top 50 money winners. Absent was Annika Sorenstam, who opens her defense of the U.S. Women's Open on Thursday at Pine Needles in Southern Pines, N.C.