Choi's 68 took her to 13 under par after a rain-affected third round, but Park scored six birdies in seven holes on her back nine to card a 65 and move into contention.
Australia's Karrie Webb will also be in the final trio on Sunday after her 68 moved her to nine-under.
Suzann Pettersen leads the European challenge on eight-under, but she could not maintain her momentum after a second-round 64 - she dropped three shots on the 15th and 16th holes to damage her chances.
Play was delayed for over four hours because of rain and lightning.
- Karrie Webb