Haru Nomura grabbed the lead in the LPGA Texas Shootout near Dallas on Friday, her eight birdies more than offsetting two bogeys in a 65 that left her one shot in front of Ariya Jutanugarn.
After playing the front nine at Las Colinas Country Club in one-under par, Japan's Nomura caught fire coming in. She made six birdies in eight holes before capping her round with a bogey at 18 -- still good enough for the halfway lead on nine-under par 133.
"My mind was very calm today," Nomura said. "It was very windy, but I like windy and tough conditions. I putted well and shot pretty good today."
Thailand's Ariya posted her second straight 67 for sole possession of second place on 134 -- one stroke in front of Norway's Suzann Pettersen, who signed for a 65.
"Pretty good today," said Ariya, who is closing in on the world number one ranking of New Zealand's Lydia Ko. "I hit the ball pretty good on my front nine, made some putts today."
Elder sister Moriya Jutanugarn was in a group sharing fourth on 136 after a 66 that included a hole in one at the par-three 13th. She used a nine-iron to make her second ace of the year.
"I can hit it pretty straight, so it should usually be pretty close," Moriya said. "It was lucky, but it was also a good shot."
Moriya was joined on 136 by South Korean star Park In-Bee (67) and American Marina Alex (69).
"I like this golf course," said Park, a two-time winner at Las Colinas. "I was putting really good on these greens when I was winning, so hopefully I can drop some more putts on the weekend."
Another pair of sisters, Nelly and Jessica Korda, were in a group on 138.
Dori Carter headed a group on 139 after a course-record 63 - a 13-shot improvement over her opening 76.
"You know, that's just golf," Carter said. "I struck the ball well yesterday and I didn't get up and down. Today I did."
Ko endured a difficult day. The world number one carded a one-over par 73 to fall into a tie for 47th.