The American star shot 65 to finish on 16-under.
South Korean Jiyai Shin, who broke the tournament record with a nine-under 62 in the first round on Friday, shot 69 and now stands second having led the opening two rounds.
Tied for third four strokes off the lead are Dewi Claire Schreefel (69) and Danielle Kang (70).
Ai Miyazato, looking to end a brief victory drought, is tied for fifth with Stacy Lewis and Azahara Munoz.
- Dewi Claire Schreefel
- Danielle Kang