England's Karen Stupples relinquished her one-shot lead at the Kraft Nabisco Championship as she carded six bogeys for a second-round 67 at Mission Hills.
Stupples was unable to maintain her early form at the first women's major of the season, dropping to two-under for joint-seventh place in California.
Lorena Ochoa took advantage with a one-under 71 to move joint top of the board with Heather Young on five-under.
Maria Hjorth and Mi Hyun Kim shot 70s for joint third place on four-under.
Hee-Won Han (69) and Sweden's Annika Sorenstam (70), who is aiming to win the event for the fourth time, were two shots further back.
Defending champion Morgan Pressel shot a 74 and now lies 22nd at one over.
World number one Ochoa insisted patience was the key for her move into joint pole position.
"I kept telling myself just to 'be patient and you're in position and you have a couple more rounds," Ochoa said.
"I'm in the right position, just where I like to be starting the weekend."
"I hit the ball really well and gave myself a lot of birdie chances. Now it's a matter of having faith for the next couple days."
American joint-leader Young, who carded carded a two-under 70 admitted: "It feels good to be there but it's just halfway.
"I don't have any expectations for the weekend, just to try and keep my head up.
"Lorena's playing phenomenal golf. I expect her to out-drive me on every hole, so I'll have a lot of shots into the green first."
The other women's majors are the LPGA Championship (5-8 June), the US Women's Open (26-29 June) and the Women's British Open (Sunningdale, 31 July-3 Aug).
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