South Korea's Kim Sei-young fired a second-round 65 on Friday to charge into the weekend at the Thornberry Creek LPGA Classic with a four-shot lead on 16-under par 128.
Kim's 36-hole total was a tournament record, four strokes better than Australian Katherine Kirk's halfway total en route to victory last year.
It matches the lowest 36-hole total on the LPGA Tour this year.
Kim teed off on the 10th hole on the par-72 course in Oneida, Wisconsin, and birdied her first four holes.
"First hole, my second shot was almost a tap-in birdie, so (I) started really solid," said Kim, who is seeking a seventh LPGA title. "After that, every hole I made really close to the pin. So I had a lot of birdie opportunities and I putted really well today."
After a brace of birdies at 15 and 16, Kim stumbled with a double bogey at the par-three 17th, but strung together three more birdies on her inward run.
She was four strokes in front of China's Liu Yu, who posted a career-best score of nine-under par 63 for a total of 132.
It was a further stroke back to South Koreans Amy Yang and Chun In-gee, overnight leader Kirk and Americans Mariah Stackhouse and Emma Talley.
Kirk had led by one after a first-round 62, but she couldn't get it going on the greens Friday and settled for a 71.
The Australian veteran hit 16 of 18 greens in regulation but needed 33 putts and made just two birdies.
"Front nine, I just couldn't get one to drop, and back nine, hit lots of good putts and, again, nothing happened," Kirk said. "Overall, I'm happy with how today went. I was very patient. I hit a lot of greens. That's all you can do."
Liu, seeking her first LPGA win, rolled in a 15-foot eagle putt at the par-five third that she said "kind of got me going."
"It doesn't feel too dramatic actually," said Liu, who added seven birdies in a bogey-free round.
"I wasn't hitting it too spectacular, but I was rolling a lot of putts in. So that was the major difference today than yesterday," added the rookie, whose best LPGA finish was a third-place at the weather-shortened Texas Classic.
Kim Sei-young's 36-hole total of 16-under par 128 was a tournament record at the Thornberry Creek LPGA Classic