It was also a measure of redemption for Clark, who last year smashed a locker at Oakmont after missing the cut in the US Open.
He was forced to take anger management therapy, pay for the damages and contribute to a club-picked charity to avoid being banned from the site of the 2033 US Open.
"What happened last year at Oakmont wasn't the greatest thing," Clark said.
"The greatest thing about having a downfall like that is the comeback and today feels really special after having a really tough year and grinding it out."
Clark said that his confidence levels were "definitely getting back to where they were" after birdies on four of the first six holes and playing the last eight holes in seven-under to overtake Kim, who began the day with a two-stroke lead.
The 30-year-old from Seoul, seeking his first victory since the 2023 Sony Open in Hawaii, made 33 birdies for the week but could not overcome Clark's birdie onslaught.
Clark sank a 21-foot putt at the second hole and a 15-footer at the sixth, before his sensational finish.
Clark reached the green in two at the par-five 12th and holed a 15-foot eagle putt, added a birdie putt from just inside 45 feet at the par-three 15th, rolled in a 12-footer for birdie at the par-three 17th, and another from inside three feet at 18.
Kim birdied four of the first seven holes before a three-putt bogey at the eighth.
He then reeled off three birdies in four holes starting with a 16-foot putt at 11 but still could not match Clark.A