Andrea Lee of the United States grabbed a two-shot lead at the halfway stage of the BMW Ladies Championship in South Korea on Friday.
The 24-year-old shot her second consecutive bogey-free round for another six-under-par 66 in Wonju, the lone LPGA stop in South Korea this year.
Lee is at 12-under after two rounds, two strokes ahead of three players – world No 2 and overnight leader Atthaya Thitikul, local amateur Kim Min-sol and American Lilia Vu.
New Zealand's Lydia Ko was in tied fifth, four shots off the lead.
It was another disappointing day for world No 1 and defending champion Ko Jin-young of South Korea, who carded a 79 following her 80 on Thursday. Ko is returning from two months out with a wrist injury.
Thailand's Thitikul could replace her at the top of the world rankings with a victory this week.
Halfway leader Lee, who was born in Los Angeles to South Korean immigrant parents, said playing in her parents' native country carried a special meaning.
"Just to be here and to play in Korea for the first time means a lot," she said, according to Yonhap news agency.
"And if I were to be able to cap it off with the win, it would be even more special."
The BMW Ladies Championship has a purse of $2 million.