Cam Davis has continued his welcome return to form as he eyes a big pay day at the PGA Tour's $31 million RBS Heritage signature event.

Coming off five straight missed cuts, including the Masters, 30-year-old Australian Davis backed Friday's 66 with a four under 67 at Harbour Town on Saturday to be five shots behind leader Si Woo Kim entering the final round.

South Korean Kim didn't make a bogey until the final hole as he posted a 66 to reach 15 under and lead by a shot from overnight frontrunner Justin Thomas (69) and Andrew Novak (66).

"I played great — only missed the last hole, so that's not a big deal," Kim said. "So I play pretty much 35 holes really decent. So I'm not going to worry about the last hole for tomorrow. I'm in good position. I've been playing good."

Of the other Australians, Adam Scott shot a 69 to be six under and tied 28th alongside Jason Day (70) and rookie Karl Vilips (71) while Min Woo Lee (71) was well back at one over.

Two-time major winner Thomas had a most interesting day that ended with a 15-foot birdie as he seeks a first win since since the 2022 PGA Championship.

Thomas was assessed a one-shot penalty from a waste area on the par-5 second hole when he notified a rules official that his ball moved a fraction while he was removing some loose gravel around it.

Then on the 11th hole, he tried to splash out of some shallow water in a hazard and muddied his shirt and face. The ball moved 15 yards.

"That didn't seem worth it," Thomas said, loud enough for the gallery to hear and to laugh.

Novak, an athletic player who has had three close calls at his first PGA Tour win, played without a bogey and missed plenty of good birdie chances. He did well enough to get into the final group with Kim.

Maverick McNealy shot 64 and was alone in fourth, two shots behind. He was followed by former British Open champion Brian Harman (66) and Tommy Fleetwood, who had three birdies over his last six holes for a 68.

Defending champion Scottie Scheffler had a rough stretch early on the back nine that derailed his momentum, though he still managed a 68 and was very much in the game at only four shots out of the lead.

This is a signature event with no cut and the scoring average has been roughly the same all three days. It's a matter of gets on a roll, who holes putts and who limits mistakes.

Thomas has said he is capable of ending his three-year drought and simply needs the tournament to unfold instead of forcing the issue.

This was only a 69 but important to him because he managed a round under par when it felt like nothing was going right.

And that birdie on the last hole?

"It was huge," he said. "I played really well today, really solid. Just didn't have much to show. The course is getting very difficult, very firm and fast. ... It's nice to finish off like that and ride that momentum into tomorrow."

- with AAP