Thailand's Ariya Jutanugarn carded a five-under 67 to secure a four-shot lead heading into the final round of the US Women's Open.
After the rain-hit second round spilled over into day three, the 22-year-old had to play 28 holes, firing six birdies and a solitary bogey during the penultimate round to sit on 12-under overall.
Speaking after the marathon day at Shoal Creek, Jutanugarn told LPGA.com: "I told myself to just go out and have fun and be really committed, and I did.
"My putting has been working pretty good. I didn't hit my tee shots very well, but it was a fun day."
Having set the pace after round two, back-to-back bogeys on an otherwise faultless round left Australian Sarah Jane Smith in second place on eight-under for the week.
Smith had held a three-shot lead but endured a frustrating Saturday, carding 16 pars and bogeys at the eighth and ninth while Jutanugarn closed the gap and eventually passed her - they had been tied for the lead after Thursday's opening round.
Two shots further back is South Korean Hyo Joo Kim, a bogey on the par-three fifth hole the only blemish on her round of 68.
Sweden's Madelene Sagstrom and Spain's Carlota Ciganda lead the European challenge, but both are in a tie for fifth, some eight shots behind Jutanugarn.
England's Jodi Ewart Shadoff mixed three bogeys with two birdies to shoot a round of 73 and tie for 14th, while compatriot Charley Hull is a shot further back on one over par overall.