Ji Eun-hee went one shot clear at the LPGA Championship with a three-under round of 69 in New York.
The South Korean picked up strokes at holes two, five, six, 11 and 15 but had two bogeys to balance against that.
It was a big turnaround for Ji, having shot a three-over 75 on day one.
Karrie Webb is one shot back in second after signing for a 68, picking up five birdies after a bogey at the first.
A pack of four sits two off the lead, consisting of Stacy Lewis, Giulia Sergas, Park In-bee and Suzann Pettersen.
Overnight leader Pak Si-ri fell well out of contention with a three-over round of 75.