Chella Choi posted a 4-under 67 on Friday to take a 1-stroke lead after two rounds of the Jamie Farr Owens Toledo Classic.
Choi, who is winless on the LPGA Tour, completed 36 holes at 9-under-par 133.
Evian Masters winner Inbee Park fired 6-udner 65 to move into a share of second place at minus-8 at Highland Meadows Golf Club.
Park was joined by Hee Kyung Seo (66) and Mika Miyazato (68).
First-round leader Pernilla Lindberg managed an even-par 71, but slipped into a tie for fifth at 7-under-par 135. Lindberg stands alongside 2011 U.S. Women's Open champ So Yeon Ryu (68), Hee-Won Han (67) and Karine Icher (69).
Choi got going with a birdie on the first. Three holes later, she converted another birdie effort to move to 7-under. Choi birdied the par-5 seventh to get to minus-8 and she remained there until the 10th.
The 21-year-old Korean faltered to bogeys on 10 and 11 to slide back to minus-6. She got one stroke back with a birdie on the 13th.
Choi jumped into the lead with back-to-back birdies from the 15th. Those birdies got her to 9-under and she parred the last two holes to end there.
"I play really good today. Same as yesterday. Shot it really good today," Choi stated.
Park played the back nine first on Friday and picked up birdies at 11 and 13. After converting a birdie effort on the 15th, she made it two in a row with another birdie at 16.
She ran off three straight pars around the turn. Park again converted consecutive birdie chances at two and three to move to minus-8. She finished her bogey-free round with six pars in a row to end one back.
"I think everything went well today. I hit the ball great. I was able to hole a lot of putts today," Park said. "Yesterday, I left some out there, but today the greens were rolling a little bit better than yesterday afternoon because it was a little bit bumpier yesterday."
Seo tripped to a bogey on the second, but erased that mistake with a birdie on the third. She had back-to-back birdies from the sixth and again from the 12th to get to 7-under. Seo birdied the last to get within one of the lead.
Miyazato had two birdies and two bogeys on the back nine to start her round. On the front side, she vaulted up the leaderboard. She birdied the third, then poured in three consecutive birdie tries from the sixth to jump to 9-under.
However, at the last, Miyazato stumbled to a bogey, which cost her a share of the second-round lead.
NOTES: Na Yeon Choi is considered the defending champion as this event was last played in 2010. She managed an even-under 71 and is tied for 47th at minus-1...The cut line fell at even-par 142...Women's world No. 1 Yani Tseng also shot 71 to miss the cut by a shot at plus-1...Also with the weekend off will be Michelle Wie, Anna Nordqvist, Ai Miyazato and Morgan Pressel.