Park produced a bogey-free round at the Mission Hills Country Club and has suffered only two bogeys thus far in the first major championship of the year on the LPGA Tour.
She turned in a 54-hole score of 12-under-par 204 and will begin Sunday's final round with only one player closer than six shots back.
Lizette Salas, who started the third round two shots behind Park, wound up three off the pace at 207 after shooting a 68.
Park, the youngest player to win the U.S. Women's Open, has four career victories on the LPGA Tour and is seeking her second title of 2013. She won a tour stop in Thailand six weeks ago.
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