It was Na's second PGA Tour title but his first since 2011 and he was understandably emotional afterwards especially given how many times he had come close to winning since his breakthrough at the 2011 Justin Timberlake Shriners Hospitals for Children event in Las Vegas.
He's had three dozen top-10 finishes since that last win and showed signs earlier this year that reaching the top again was still well within reach.
Na shot a final-round 6-under 64, highlighted by five birdies on his first nine holes.
Kraft said he struggled judging the speed of his putts. Varner shot 72 and finished tied for fifth at 12 under along with Cook (66), Joaquin Niemann (64), Sam Saunders (70) and Joel Dahmen (69). Stallings finished his day tied for 13th at 9 under; Kevin Na is in 1st at 19 under; Kelly Kraft is in 2nd at 14 under; and Brandt Snedeker and Jason Kokrak are tied for 3rd at 13 under. He has one top-10 finish in each of the past two years and won the Australian PGA Championship in 2016.
"It feels awesome. I see the record every time on TV - the most top fives, the most top 10s without a win", he told CBS. His second PGA Tour win appears imminent.
The only drama down the stretch was who would pick up the last of the tournament's four qualifying spots to the British Open in two weeks.
Before teeing off on the par-four seventh he stepped on a tuft of grass, which he later told rules officials was in his preferred line, leading to the penalty. Varner would birdie holes 11,12, 14, and 17.
He sank a five-foot birdie putt at the fourth and one twice as long at the fifth before dropping a 32-footer at the sixth.
"Tough to describe how wonderful this feels", Knox said.
The Old White TPC dried out on a sunny Saturday and scores weren't as low as the first two days when rains softened the course and yielded eight rounds of 63 or better.
Knox is set to climb into the top 50 of the World Golf Ranking and has boosted his chances of making Europe's Ryder Cup team in September.
The five-time major champion had three bogeys, a double bogey and a triple bogey on 18 to go with four birdies for a final-round 74 to finish the tournament at 279 and tied for 65th place.