Park, who led by a single stroke over Spain's Carlota Ciganda at the halfway stage, increased her advantage as Ciganda, whose third round 74 was 11 shots worse than the previous day's effort, slipped back with the tournament heading to its conclusion.
The Spaniard led by three as she headed for the sixth tee having birdied two of the first five holes, and by one at the turn, but a triple-bogey seven on 17 left her off the pace.
Park, who took six at the par-five first, carded five birdies on the back nine one her way to a three-under-par 69 to leave herself two shots ahead of Suzann Pettersen.
The Norwegian's second successive round of 67 took her to 12 under, two shots ahead of Park's compatriot Soo Jin Yang with Ciganda a further two strokes back.
Koreans were well represented at the top of the leaderboard with Hyo-Joo Kim and Bo-Mi Suh among four players tied for fifth place on seven under.