"I only had a gap wedge in, it was kind of in the shadows, you can't see the pin as well at that time of the day. I couldn't see the ball go in.
"After that I set up two birdie opportunities and I was able to feed off that."
Ko is in a tie for fourth place at 11-under, with Lexi Thompson and Caroline Masson also ahead of her at 13-under. Ko is eying her 24th career win and second of the 2022 season.
There is a host of players in contention with defending champion Nasa Hataoka and fellow top 10 players Thompson and Brooke Henderson among those within striking distance.
The 19-year-old American Li is chasing her first big win. The former child golfing prodigy has a couple of victories on the LPGA's development tour this year.
Li was two-over through seven holes and quickly fading from the picture when she responded with five birdies over the next 10 holes to regain the lead and set up a final round filled with possibilities.
"I was probably a little nervous. It wasn't anything crazy, but haven't felt nervous in a long time," Li said. "Actually making those bogeys might have helped a little, just getting that out of the way and knowing that I could just freewheel it out there a little."
Li was at 14-under, and the final group offers a pair of prodigies.
Thompson was 12 when she first qualified for the US Open at Pine Needles. Seven years later, Li broke her record when she qualified for the 2014 Open at Pinehurst No 2.
"It'll be great," Thompson said. "I played with her a little bit — not so much out here. But I think everybody knows how amazing of a player she is. Just speaks wonders to the amount of work that she's put into her game, just the amount of talent she has."
This week already has felt like a bonus for the California teen. Li secured her LPGA Tour card for next year with two wins and a runner-up finish on the Epson Tour, which offers LPGA cards to its leading 10 players.
Li received a sponsor's invitation in Canada last week and tied for ninth in the CP Open, which got her into the field in Ohio. Now she has a chance to win and join the LPGA Tour for its final two months of the season.
But it will require navigating through a traffic jam of key players, a list that includes four major champions.
For Thompson, the No 7 player in the world, it's another chance to end more than three years without winning.
"It has not worked out the way I want it to in a few events, but that's golf," Thompson said. "I think you never lose; you're always learning. There is always something to build on and learn from those days.
"It's golf. I mean, it's a crazy game. It can be with you one day and not the next."
- With AP