South Korea's Sei Young Kim fired a 7-under 64 on Friday and holds a one-shot lead at the midway point of the Marathon Classic in Sylvania, Ohio.
Jeongeun Lee6 shot 66 to make it two South Koreans at the top of the leaderboard in the Toledo-area event.
Jennifer Kupcho (66), Lexi Thompson (67) and Stacy Lewis (68) are two shots behind Kim, who is at 11-under 131 after two trips around Highland Meadows Golf Club.
Kim, who shot a 67 in the opening round, fired seven birdies in a bogey-free day, including four in a row from Nos. 3 to 6. She was especially pleased with her putting.
"It was pretty good, because greens are very pure, so if I get a really good read, it works," Kim said after the round. "So, yeah, I just (had) good work with my caddie."
Lee6 made six birdies, but a bogey on the par-4, 12th hole prevented her from sharing the lead.
The U.S. Women's Open champion feels the course is suited for her game.
"It was pretty good. The course, you know, the green was not too soft, not too firm," Lee said through her translator. "It was pretty good so far. It was so easy to play with my second shot in order to control my shots so far. Satisfied with it."
Spain's Carlota Ciganda (68), Clariss Guce (68) of the Philippines and South Korea's Youngin Chun (70) are tied for sixth, three shots behind Kim.
Ciganda is attempting to end a victory drought that stretches back to November of 2016.
"To be honest, I didn't think I was going to play very good this week," Ciganda said. "It's golf, and I think I didn't think too much about the results, so I'm happy to be where I am. I have two more days. I really like the golf course. It's in great shape, and it's always nice to play here."
Germany's Caroline Masson and Spain's Azahara Munoz are four shots back. Both women shot 70.
Canada's Alena Sharp, who was tied for the first-round lead with Chun, slid into a tie for 11th after shooting 1-over 72.
Kupcho had six birdies and one bogey during her round, Thompson made four birdies and Lewis had five birdies and two bogeys.
"The golf course is in amazing shape for us, as usual," Thompson said. "It's a great test of golf. Some of the tee shots you really have to commit to the lines.
"I play it pretty aggressively. I don't hit too many drivers, but at the same time, I take aggressive lines with my 3-wood."
Thompson also is feeling recharged. She didn't play the past two weeks after tying for 26h place at the KMPG Women's PGA Championship.
"It was very much needed," Thompson said. "I played five weeks straight before that and was just mentally drained. I had two majors in that five-week stretch, and really my whole career I've never played five weeks straight.
"It was a lot different for me, and I needed those two weeks off to unwind. I didn't touch a club for the first week, and then slowly got back into it the second week. Just didn't really over-practice. Just feel a lot more refreshed."
Defending champion Jasmine Suwannapura of Thailand is tied for 64th at even par after shooting 72.