Park, who was in front by a single shot after Friday's second round, finished the day at 14-under-par 199, two better than a pair of pursuers.
Park is seeking her second career LPGA victory and first since the 2008 U.S. Women's Open.
Tied for second at minus-12 were Brittany Lang and Hee Kyung Seo, each of whom registered 4-under 67s.
Grabbing sole possession of fourth place was Anna Nordqvist (67) at 10-under 203. Shanshan Feng (70) and first-round leader Sandra Changkija (69) shared fifth at minus-9 with Karin Sjodin (69) and Nicole Hage (67).
Rain delays necessitated seven players completing their second rounds Saturday morning before the third round went off scheduled.