Park, the No. 2 player in the world according to the Rolex World Rankings, is bidding for her fifth victory of the season.
Park took control with birdies at the par-3 16th hole after hitting a 7-iron to three feet and making a six-foot putt at the par-5 17th.
Australian Minjee Lee, 19, the second-round leader who is bidding to win her second LPGA title, shot 75 and fell into a tie for ninth.
Kim, who clinched the 2015 LPGA Rookie of the Year award with her third victory of the season two weeks ago, shot 70.