Still only 20 years old, Kim - nicknamed Tom after his boyhood love of Thomas the Tank Engine - became the second-youngest player in PGA Tour history to capture multiple titles.
The South Korean fired a five-under par 66 to finish 72 holes at TPC Summerlin on 24-under 260, having not made a single bogey all week.
That was good enough for a three-stroke victory over Americans Cantlay and Matthew NeSmith, although the former was actually tied for the lead on 24 under heading to the 18th before sending his tee shot at 18 into a bush in a dirt area left of the fairway.
The end result was a nasty triple-bogey after Cantlay decided to risk blasting out of the hazard rather than take a penalty stroke, only for the ball to stay firmly lodged in its hiding place.
That saw the 20-year-old from Seoul, who won his first PGA title at Greensboro in August, wrap up yet another victory on the PGA Tour.
"I played really solid this week," champion Kim said. "We had a really good game plan going into the week and it paid off.
"I've worked really hard and my team has worked really hard. I'm just really grateful and very fortunate to have an opportunity like this. I'm having fun playing on the PGA Tour. It's awesome."
As for Cantlay, he could do little but rue the shot that cost him a chance at victory.
"I made a bad swing and it went where it went," he said. "After it was kind of in the bush there, I figured the only chance I had to stay in the tournament was to try and get it back in the fairway. I couldn't get it back in the fairway."
On not taking the penalty, he added: "I figured it was worth the risk because I didn't think I'd have too much of a chance of getting it up and down from the brush there.
"I played well all week for the most part apart from one bad swing at the end. Would have liked to have closed the deal out but sometimes that's golf.
"Obviously the last hole makes the whole week kind of sour."
Kim added: "I got very lucky on the 18th. I'm not going to lie. Patrick played awesome and it was an honour to battle with him. To come out on top, I feel very fortunate."