The South Korean notched up a seven-under round of 67 to take a two-shot lead into the second round, with compatriots Na Yeon Choi, Inbee Park and Sei Young Kim next best.
Kim, who started on the back nine, began in indifferent fashion, bogeying the 11th. However, it would prove her only drop shot of the day as she went on to notch up eight birdies, including four in her last five holes.
It was Choi who had held the lead for much of the day after producing the best round of the morning starters, with Park and Sei Young Kim later joining her atop the leaderboard, only to be surpassed by Kim who was in the day's final pairing.
Local favourite Michelle Wie began her title defence in strong fashion, reaching the 15th on three-under, but a bogey at the 17th saw her slip to five off the pace.