The 27-year-old South Korean sank a 13-foot putt on the final hole to shoot a two-under-par 69 and stretch his lead in the PGA Tour event to two strokes after Saturday's third round at Palm Harbor, Florida.
"It has been a while since I've been in the lead like this, and I'm sure I will be nervous," Im said. "But the best I can do is just to play my own game."
Im had gone nine holes without a birdie on Innisbrook Resort and Golf Club's tough Copperhead Course before sinking his last birdie attempt.
The 27-year-old enters Sunday's final round at 11-under 202 in search of his third PGA Tour win and first since the 2021 Shriners Children's Open.
Veteran Brandt Snedeker posted 67 to pull into a share of second place with fellow American David Lipsky, who turned in an erratic 70.
"I'm going to enjoy my late Sunday round tomorrow and go have some fun," said 45-year-old Snedeker, who will be seeking his 10th PGA Tour win and first since the 2018 Wyndham Championship.
Snedeker's bogey-free round -- beginning with three birdies on the first four holes -- matched the best rounds of the day.
Without a win on the tour, Lipsky's round included five birdies and four bogeys.
"The short game and the putter really saved me and kept me in it," Lipsky said, planning a visit to the driving range "to try to fix for (Sunday)."
England's Marco Penge and England's Matt Fitzpatrick shot matching 68s to hold a tie for fourth place at eight under.
Fitzpatrick finished a shot behind champion Cameron Young in last weekend's The Players Championship after leading going into the final round.
The lone Australian to make the weekend rounds, Karl Vilips shot a one-over 72 to be tied 48th and will be ruing a double bogey at the last hole.
25°C