Lexi Thompson, seeking her first
Thompson, a 19-year-old Floridian, made four birdies on the front nine at Mission Hills Country Club in Rancho Mirage to reach 14 under par for the tournament.
Michelle Wie, who started the day tied with Thompson for the lead, and Se Ri Pak of South Korea were tied for second place at nine under.
Wie, also seeking her first major and first
The 24-year-old made bogey on the par-four third hole and three-putted for another bogey at the par-three eighth hole.
And on the par-five ninth hole, Wie missed a seven-foot putt for birdie and settled for par, while Thompson, her playing partner, sank an eight-footer for birdie.
Christie Kerr was at seven under for the event. Gerina Piller, former Kraft Nabisco winner Stacy Lewis and first-round leader Shanshan Feng of China were tied at six under.