American Lizette Salas had eight birdies in an eight-under par 64 on Saturday to take a two-stroke lead heading into the final round of the US LPGA tournament in Indianapolis.
Salas, who began the round tied for the lead with Park Sung-hyun and Ko Jin-young, had a 54-hole total of 21-under 195.
She was two shots clear of Park and South Korean Amy Yang, with defending champion Lexi Thompson alone in fourth a further three strokes back.
Park, who has a chance to topple Thailand's Ariya Jutanugarn from the number one world ranking with a victory this week, had racked up eight birdies and was 21-under and in the lead when she double-bogeyed the par-four 16th, hitting her approach shot into the water.
The two-time major winner, seeking her third win of the season, parred the last two holes to complete a six-under par 66 that left her tied on 197 with Yang, who had seven birdies without a bogey in her 65.
Thompson climbed the leaderboard with an eight-under 64, her eight birdies including four in a row from the fourth through the seventh holes.
Rookie of the year contender Ko, who returned the waterlogged Brickyard Crossing Golf Course to complete her second round on Saturday morning, had five birdies and three bogeys in her third round 70 and shared fifth place on 201 with Japan's Nasa Hataoka (68) and Mina Harigae (65).