A double bogey and a bogey on the seventh put the South Korean three shots over at the turn and although she made three birdies on the way back, another bogey on the 15th saw her sign for a 73 to be six-under on 210.
That allowed Sweden's Maria Hjorth to close the gap with a round of 71. She was guilty of three bogeys, but made up for it with birdies on the first, third, 11th and 12th holes.
American Cristie Kerr was two shots further back in a tie with Seon Hwa Lee of South Korea.
Laura Diaz had the best round of the day, her 69 sending her into sole possession of fifth place, ahead of a three-way tie for sixth that included In-Kyung Kim, Morgan Pressel and Katherine Hull.
After the third-round cut, former Scottish Ladies' Open champion Gwladys Nocera scraped through with a single shot to spare on 221.
Mhairi McKay was one of the casualties at that stage on 229, with fellow Scot Janice Moodie having bowed out at the halfway point on 159.