American Angel Yin holds a two-shot lead after firing a three-under-par 69 in her second round of the CME Group Tour Championship in Florida.
After an impressive round of 65 on Thursday, Yin built further momentum to nudge South Korea's An Na-rin into second.
The winner of the LPGA's season-ending event at the Tiburon Golf Club will take home $4m (£3.2m) in prize money.
An struggled to find her rhythm with two bogeys and two birdies leaving her to sign for a par round of 72.
South Korea's Choi Hye-jin is tied with An on eight-under after a second successive round of 68.
A group of five, including American Nelly Korda, sit two shots further back on six under.
Korda, who came from behind to win The Annika last week, put in a vastly improved showing, enjoying a six-under-par round to quickly move on from an opening round par score.
England's Charley Hull also went round in a six-under-par 66 but Thursday's one-over-par 73 leaves her with work to do over the final two days.