They headed Spaniard Carlota Ciganda (69) by one stroke, while New Zealander Lydia Ko matched the best score of the week (66) to vault within two shots.
Defending champion Danielle Kang (69) had moved two shots of the lead before a pair of bogeys on her final three holes left her four back.
A day after feeling that a three-under 69 did not reflect how well she had played, Ryu admitted an identical score on Friday was perhaps more than she deserved.
"Golf is definitely a funny game because yesterday I thought I hit it just really, really perfect, like I just couldn't ask more, and I shot three-under," she told reporters.
"And then compared to yesterday, I felt like I absolutely hit it everywhere out there but still shot three-under.
"That was really good learning (experience)."
Ryu ended a nearly year-long victory drought when she won the Meijer Classic two weeks ago, a result she achieved after a change in attitude.
LATE BIRDIES
Ryu, who in Cameron McCormick uses the same coach as Jordan Spieth, said she had picked up some extra length recently.
It certainly came in handy on a course that is still drying out after being drenched earlier in the week.
Ryu finished with three birdies in the final five holes to catch Park, who faltered with a bogey at her 16th hole, the par-five seventh.
Park's second shot from more than 200 yards landed pin high but took a huge bounce over the green, from where she hit a poor chip that almost trickled into a water hazard on the other side.
Henderson, in the hunt for her second victory in the event after beating Ko in a playoff in 2016, banged in a 15-foot birdie at the last to earn a share of the lead.
"Up and down all day," she said of a round that included five birdies and four bogeys.
"The birdies are a good sign, the bogeys not so much. But it was kind of playing tough early this morning, it was really windy, and it just took a couple holes to kind of adjust to that."
Meanwhile, South Africa's Lee-Anne Pace was disqualified for using a non-conforming club.
She damaged her sand wedge when slamming it against a stake but did not realise she had done so until she had used the same club again a few holes later.
(Reporting by Andrew Both; Editing by John O'Brien)
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