Se Ri Pak shot an eight-under 64 to take a one-stroke lead over Sweden's Sophie Gustafson after two rounds of the Longs Drugs Challenge in California.
Se Ri Pak had a superb second round
The Korean, second to Sweden's Annika Sorenstam on the LPGA money list, eagled the par-five eighth with an 18-foot putt.
She also managed seven birdies in setting a tournament record of nine-under par 135.
"My game is getting more consistent and that's good at the end of the season," said Pak, who has two wins this year.
"Yesterday, I was struggling and my game was out of control. Today, I struggled early, but I started to chip and putt better, and I was playing really good."
Gustafson had three birdies in a two-under 70 that followed
her opening 66.
"I wasn't playing half as good as I was yesterday," said Gustafson. "I didn't hit many fairways, which meant that I couldn't reach any of the par-5s."
Jamie Hullett, Suzann Pettersen, Wendy Ward and Michelle Ellis are tied for third place on five-under.