Stacy Lewis, a two-time winner this year, and US Women's Open champion So Yeon Ryu shot 64 to tie for fifth at 15 under. Lewis opened with a 72, then shot 64-69-64.
"Yeah, if I could go back and redo round one, I think I would be in a little better spot," Lewis said. "I'm just proud of the way I came back and finished it out really strong."
China's Shanshan Feng, coming off a major victory two weeks ago in the LPGA Championship, was another stroke back along with Anna Nordqvist. Feng had a 66, and Nordqvist a 67.
Michelle Wie tied for 68th at 3 over. She shot a 74.