Denmark's Nanna Koerstz Madsen fired a five-under-par 67 on Friday to assume a two-shot lead at the JTBC Classic in Carlsbad, California.
Madsen, who opened with four birdies on the first five holes, sits at 11-under 133 through 36 holes at Aviara Golf Club.
New Zealand's Lydia Ko (67) and South Korea's Hye-Jin Choi (68) are tied for second at nine under, two shots back. Lydia Ko won the Carlsbadevent in 2016.
First-round leader Jin Young Ko of South Korea shot a one-under 71 to drop to a tie for fourth-place alongside compatriot Na Rin An (67) and Canadian Maude-Aimee Leblanc (68) at eight-under.
Leona Maguire made five birdies but a costly double bogey on 10 restricted her to a two-under 70 and a share of ninth on five-under par alongside defending champion Inbee Park and six others.
Stephanie Meadow, who had been level with Maguire after the first round, shot level par in an up and down round that featured five birdies and as many bogeys. She is now in joint 20th on three-under.
Madsen, who fought off two bogeys on the day, said her win at the Honda LPGA Thailand two weeks ago has been a confidence-booster.
"Yeah, I figured out this year. I haven't figured out the other years," Madsen said.
"I'm definitely playing better this year than I've done previous years I played. I have confidence out there winning like two weeks ago.
Yeah, making a ot of good putts and hitting a lot of greens."
