Breakthrough winners in their last starts, Sei Young Kim and Ally McDonald were on top again in the Pelican Women's Championship.
Ko carded a near ideal third round 66 to sit at seven under and fourth overall, with a double bogey on the 13th hole the only blemish on her scorecard.
The South Korean, who won the most recent major - last month's Women's PGA Championship - hit a third-round 64 to take a five-shot advantage into the final round. Popov, 28, won her first and only LPGA event so far, in August when she was the surprise victor at the Women's British Open.
Kim came into the third round with a one-shot lead over McDonald then used the birdie run to leave the American behind in the first year tournament which was originally scheduled for May.
"I grinded it out and I made a lot of par putts coming in, so I'm pretty happy with my score", the German said. It could be that she chased me down, that was my thought.
South Korea's Kim caught fire on the back nine, making birdie on four straight holes from the 14th through the 17th to reach 14-under 196 at the Pelican Golf Club in Florida.
Popov was kept in contention with some solid putting including a trio of puts from between 10-15 feet which helped her make a level-par 70. Kim made her move on the back nine with four birdies, while McDonald fared well early with three birdies on the front side. She parred Nos. 3 and 4 then caught fire on number five before ending her front nine with another birdie on the par-three ninth. "I just want to think about focus on myself and what I have to do".
"But on the back nine my feeling wasn't good, and Ally was going really good. I still smell. And then drink a little bit and feel - feels, you know, like little drunk".
But birdies on the 12th and 14th holes left her two under.
She skipped her title defence at the pandemic-delayed ANA Inspiration in September, and is returning to the LPGA tour for the first time in nearly a year.