Ai Miyazato fired an 8-under-par 64 on Friday to grab the lead after two rounds of the season-ending Group Titleholders.
Miyazato entered Friday four strokes behind overnight leaders Suzann Pettersen, Sun Young Yoo and So Yeon Ryu, before carding nine birdies against one bogey to jump in front.
"I was just really calm out there all day long and I did really good on the greens," Miyazato said in a post-round television interview. "My game is really in good shape but I still have a couple more days so hopefully I can keep it going."
The top-3 finishers in each official LPGA Tour event qualified for this event, which includes the top-31 players on the money list and the top-13 players in the world rankings.
World No. 4 Na Yeon Choi moved into second place at 9-under with a second- round 68 at the Eagle Course at TwinEagles Club, while Pettersen (71), Yoo (71), Brittany Lincicome (69) and Karine Icher (70) are tied for third at minus-7.
Yoo had a 70 on her scorecard after the round, but a review proved that she took an illegal drop on the No. 14. She was penalized one stroke for dropping below shoulder height and ended with a triple-bogey on the hole.
"This is one of those rules you don't like to apply a penalty to," rules official Janet Lindsay told the Golf Channel. "You don't see the player gaining an advantage, but it definitely was a breach of the rule and that is a 1-stroke penalty."
Ryu shot 72 to fall into a tie for seventh place with Sandra Gal and Karrie Webb at 6-under.
World No. 2 Stacy Lewis, the only player to win four titles this season, is 2-under through 36 holes. She has already secured the 2012 Rolex Player of the Year award -- becoming the first American to receive the honor since Beth Daniel in 1994 -- but needs to win the $500,000 first-place check this week to have any chance of passing money list-leader and world No. 3 Inbee Park.
Park, who has secured more than $2.2 million in earnings, shot 70 for the second straight day to move to minus-4.
Defending champion Hee Young Park rebounded from an opening-round 76 with a 68 on Friday.
World No. 1 Yani Tseng is currently 4-over, while Michelle Wie is alone in last place at plus-14.
NOTES: Miyazato's 64 marked her low round of the season ... Last year, Hee Young Park collected her first LPGA Tour victory at the season-ending event. Park fired rounds of 71-69-69-70 to win by two strokes over Paula Creamer and Sandra Gal.