Austin Ernst fired a three-under par 69 at the Drive On Championship on Saturday to grab the first 54-hole lead of her career and a one-shot cushion heading into Sunday's final round.
The 29-year-old American finished with four birdies and one bogey to reach 13-under 203 for a one stroke lead over second round co-leader Jennifer Kupcho in Ocala, Florida.
"I had to work a little bit harder than I have had to work the last couple days," Ernst said.
Kupcho, who is seeking her first LPGA win, made an eagle on her final hole for a one-under 70 to stand on 204 with a five-stroke gap to third place.
On a rainy day at the Golden Ocala course, Swiss Albane Valenzuela shared third after a bogey-free 66 that included six birdies. Patty Tavatanakit, with a 69, and American Jenny Coleman, with a 70, are also on 209.
Spain's Carlotta Ciganda (75) and Danielle Kang (69) were a further two strokes back.
Ernst, chasing a third LPGA title, started her third round with two birdies in the first five holes. She chipped in for a birdie on the par-four ninth to move to 13-under for the tournament.
"I know I need to go play well," Ernst said of the task awaiting Sunday. "I can't not play well and win, so it's going to be the same type stuff. I know what to expect. I've slept really well."
Her only blemish of the round was a bogey on the par-four 10th, but she rebounded on the next hole with her fourth and final birdie of the day.
Kupcho set the stage for her dynamic closing eagle with a fairway wood from 215 yards that just cleared the rocks and water fronting the green on the par-five 18th.
"I actually was standing on the tee and I was like, 'I feel an eagle coming on.' So, it was pretty cool to do it," Kupcho said.
"But when I got down there to the fairway I definitely didn't think it would be possible to get it close and I was not aiming anywhere close to where my ball went, but it happened to go right at the pin and carried by a couple yards, carried the water by a couple yards, and ended up in a good spot."
Laura Davies, the 57-year-old Hall of Famer, was four over after a 76. She's playing on a World Golf Hall of Fame exemption.