The 30-year-old American opened her round with a bogey but was faultless thereafter, compiling eight birdies to move onto 11 under par overall, alongside compatriot Gerina Piller and Thailand's Pornanong Phatlum, both of whom shot 67.
For the second day in a row, Piller made five birdies in an unblemished round. The 28-year-old has not made a bogey in 41 holes.
Phatlum was also flawless on Saturday and came to life after approaching the turn on one under her round. But birdies at the 10th, 12, 13 and 17th ensured she would be in a share of the lead overnight.
The round of the day came from Stacy Lewis, who is one of four players in a tie for fourth two shots behind the leaders.
Lewis came into Saturday on level par after her first two rounds, but an eagle at the third was the catalyst for a superb nine-under-par 63, which included six birdies in seven holes from the 11th hole.
She now sits alongside fellow American Lexi Thompson, Germany's Sandra Gal and Shanshan Feng of China.