South Korea's Kim wins second PGA Vegas title in a row
The 21-year-old from Seoul fired a five-under par 66 in the final round to complete 72 holes on 20-under 264 and defeat Hadwin by a stroke at TPC Summerlin in Las Vegas.
Kim sank a 12-foot birdie putt at the 15th hole, Hadwin made a bogey at the par-5 16th and answered with a closing birdie but it was too little and too late.
"Number three is so sweet," Kim said.
"It was a long day," Kim said. "I just really felt confident in myself and I was playing really well. If knew if I kind of just 'did me' I was going to be able to do it."
Hadwin's 25-foot birdie putt at 18 left him second on 265, one shot ahead of Americans Eric Cole and J.T. Poston, Sweden's Alex Noren and Canadian Taylor Pendrith.
World number 16 Kim, a runner-up in this year's British Open at Royal Liverpool, also won last year's Vegas title and the 2022 Wyndham Championship but had not been able to add to his trophy haul.
"It has been a long season," Kim said. "I'm very fortunate to defend. I've learned so much this year. It has been a blessing. It has been very humbling.
"Last year after going off such a great run, then not feeling exactly myself mid-year, it has been a grind trying to figure it out.
"It's my first full season, just trying to live up to that expectation -- great year last year, how can it get better? It has been humbling."
Kim birdied three of the first four holes before back-to-back bogeys at five and six dropped him out of the lead.
Cole, son of pro golfers Laura Baugh and Bobby Cole, fired an early 62 to set the mark to beat.
"Conditions were very good for scoring, no wind and greens were very good," Cole said. "And I switched back to an old putter today so that might have helped."
Noren reeled off three birdies in a row starting at the par-3 eighth, then birdied the par-5 13th and 16th holes to match Cole in the clubhouse.
That's when Kim made his charge, sinking a three-foot birdie putt at the par-5 ninth and six-foot birdie putts at 12 and the par-5 13th to seize the lead alone at 19-under.
Hadwin battled into the hunt with three birdies in four holes, the last after driving the green at the par-4 15th and two-putting from 24 feet to reach 19-under.
Kim answered by sinking a 12-foot birdie putt at 15 to reach 20-under and again led alone.
Hadwin found water with his second shot at the par-5 16th and made bogey while Kim sank a tense five-foot par putt to lead by two and parred 17 and 18 as well to hold off the Canadian despite his late birdie.
Hadwin, ranked 56th, took his only PGA victory at the 2017 Valspar Championship. He was also a runner-up this year to American Rickie Fowler at Detroit.