Park carded a tournament-record seven-under-par 65 on Thursday and set a new one on Saturday as she dipped a shot lower, leaving her on 18 under for the tournament.
She signed for two eagles and five birdies, with one bogey being the down point.
Suzann Pettersen, chasing back-to-back wins after her KEB-HanaBank victory last weekend, was two shots behind, with Yani Tseng the next in contention at 14 under.
"I think today [Saturday] was almost perfect for me," Park said.
"I hit the ball great and putted really good today [Saturday]. It was a perfect day. The conditions of the golf course were perfect.
"It meant I was able to go at every pin, so I was able to play aggressive."