American Noh birdied eight of the last 11 holes at Bradenton Country Club on Saturday to get to 18 under as she chases a maiden LPGA win.
Trying to win the event on a fourth venue, former world No.1 Ko birdied five of the final 11 for a 66.
American Megan Khang shot a career-best 62 to break Ko's day-old course record and sit tied for third with Jin Hee Im of South Korea at 13-under.
Australian Hannah Green managed three birdies on each side in a 66 and was tied fifth with world No.1 Nelly Korda (65), six shots behind Noh.
The 23-year-old Noh has shown she will be hand to deny on Sunday, despite the depth of talent behind her.
 "I think my tempo has been awesome this week," Noh said. "It's been the best that it's ever been. I've been really staying patient throughout not only the round, but throughout my swing."
Ko won the tournament that honours the tour's founders in 2019 at Desert Ridge in Phoenix, 2021 at Mountain Ridge in New Jersey and 2023 in a playoff at Upper Montclair, also in New Jersey. The 29-year-old South Korean player has 15 LPGA Tour victories.
"We had gusting in the front nine, so it was hard to play," Ko said. "After front nine, yeah, we made a lot of birdies, especially Yealimi. We had so much fun. I did my best today. Just some putts like was just sneaky, so I would say I kept for tomorrow."
Playing in her hometown event, Korda highlighted her 65 with a chip-in birdie on No. 9. She won a Drive On tournament on the course last year for the first of her seven 2024 victories.
"Growing up on this kind of old-school Florida grass helps because it is tough to kind of hit it off," Korda said.
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