A bogey-free round by the 21-year-old Thai star, closed with an eagle at the par-5 17th and a birdie at 18, left her level with Yin on 15-under 201 after 54 holes at Tiburon Golf Club in Naples, Florida.
"Just trying to make it the lowest score that I can," Jeeno said. "Today it's my caddie's birthday and definitely he's going to say because my birthday you shoot like a really good score.
"Hopefully I can get a big check for him tomorrow."
China's Yin Ruoning was third on 204, three strokes adrift, with England's Charley Hull and South Korean An Na-rin on 205 and American Lucy Li and Russian Nataliya Guseva on 206.
The top 60 players in the season points chase qualified for the $11 million showdown, which offers a $4 million top prize.
Jeeno seeks her fourth career LPGA title after the 2022 JTBC Classic, 2022 Northwest Arkansas Championship and this year's Dow Championship pairs event with Yin.
"Whatever is going to happen tomorrow, I take it as learning experience," Jeeno said. "It's not about life or death. It's just like what we play and then we just trying to improve ourself."
Yin, ranked 34th, won her only LPGA title last year at Shanghai.
"Felt good. The course, I think, is playing pretty tough, so happy with my score," Yin said. "I'm scoring still. Making some mistakes but saving a bunch so a lot of positives."
World number seven Jeeno opened with a birdie and added birdies at the par-3 fifth and eighth holes, then began the back nine with three consecutive birdies.
Jeeno grabbed a share of the lead at 14-under with an eagle at the par-5 17th and seized the solo lead with a closing birdie.
"Nothing specific," Jeeno said of her sizzling finish. "We know 17, it's reachable par-5, so I just trying to hit second shot on the green, which is like easy to have like easy birdie. Hit really good, went to the pin, and then not that far for the eagle.
"On 18 nothing, just trying to make par. I have no idea how I can hole that putt in as well."
'Had to keep grinding'
Yin birdied the par-3 fifth then eagled the par-5 sixth, sinking a long pitch from just off the green, and answered a bogey at seven with birdies at the eighth and ninth.
"I just knew where I needed to chip," Yin said of her eagle. "I had a good line on it and just dribbled in."
She added a birdie at the par-3 12th but stumbled with a bogey at 15 only to answer with a birdie at 17 to reclaim a share of the lead.
"I just knew I had to keep grinding it out and I needed to trust what I'm good at," Yin said. "Got a little rough, but it was good."
Top-ranked Nelly Korda, who has already clinched the LPGA Player of the Year award, closed with birdies at 17 and 18 to fire a 69.
The 26-year-old American, chasing her eighth title of the season, stood on 207 in an eighth-place pack with France's Celine Boutier, Japan's Ayaka Furue and South Korean Choi Hye-jin.
