Park finished 36 holes at 6-under 140 with Helen Alfredsson (68), Minea Blomqvist (68) and Inbee Park (68) one shot back. Defending champion Christie Kerr (69) was among those at 142, along with Paula Creamer (69).
Angela Park began play on the back nine at the Interlachen Country Club and birdied three of her first six holes. Her round was highlighted by an eagle at the par-5 second and she finished before a passing thunderstorm forced a delay in play of two hours, 27 minutes.
There were only three Americans among the top 14 with Stacy Lewis (143) joining Creamer and Kerr.
World No. 1 Lorena Ochoa, seeking her second major championship of the year, shot a 74 and was seven shots off the pace. Annika Sorenstam, who has said this will be her final U.S. Open, was at 145 after shooting a 70.
First-round co-leader Pat Hurst fell back in the pack after shooting a 78.