Park shot a second straight 4-under 68 and Ariya was better with a 67 for two-round totals of 8-under 136 at the Sky 72 Ocean Course.
Charley Hull was at 9 under at the turn after an eagle on the par-5 7th hole but dropped back after consecutive bogeys and birdied the 17th to get to 8 under with Danielle Kang. Kang was at 9 under after 11, but bogeyed 12-13-14 and climbed back, too, to share the halfway lead.
Park is preparing to be grouped over the final rounds with her main rival.
"The very first time I was grouped together with Ariya, that was when I actually felt kind of pressure or burden," Park said. "But since I've played with her quite often, I'm getting more and more comfortable with her."
Ariya bogeyed three of her first seven holes, then recovered on the back nine with six birdies, including four on the last five holes.
"I hit a few shots pretty close and I made some long putts," she said.
First-round leader Nasa Hataoka of Japan slipped to a 73, but was only two strokes off the lead along with Lydia Ko, who carded a bogey-free 68.
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