It was a wild finish at the TPC Summerlin made possible mainly by Na's mistakes.
The Ryder Cup star dropped shots at back-to-back holes before the turn but got on a roll to move away from his compatriots, gaining a stroke at the 10th to stand just a shot off the lead before reeling off four birdies in a row and an eagle two at 16.
He two-putted the par-5 16th from 40 feet for a one-shot lead after Na hit into the water and made bogey.More news: Former US President Carter falls, requires stitches
Kevin Na began the final round with a two shot lead, but Cantlay quickly inched closer with a 35-foot birdie putt at the first, but after missing his par attempt from five feet on the third, it was the Las Vegas resident who looked to be in control.
After both birdied the first playoff hole, Na sealed it with a par at the second extra hole, where Cantlay left his birdie putt almost six feet short before Na hit his four feet past. Only Brooks Koepka (four) has more wins in that span. Na rolled in his 4-foot par putt to win in Las Vegas for the second time. "I knew, I kept telling myself, 'This is the playoff I'm going to win.' And it felt great to win".
Kevin Na produced a record-breaking putting display on his way to play-off victory at the Shriners Hospitals for Children Open. He joined Jim Furyk as the only multiple winners in Las Vegas. As much as he took advantage of Na's blunders, Cantlay made some of his own.More news: Lupita Shows Off Impressive Rap Skills During American Talk Show
His 22-under total of 191 was a 54-hole record for the tournament, a home fixture for the South Korean-born American who won the first of his three PGA Tour titles in this event in 2011.
Knight had missed the cut in half of her 18 starts on the LPGA Tour and assumed she would be going back to the qualifying series. But he could get no closer than 25 feet, and his putt hung on the right edge of the putt.
Joel Dahmen ended up at 8 under, too, settling for a 64 after playing the first 10 holes in 9 under. Cantlay was just outside 10 feet - on the same line as his 25-foot birdie chance in regulation - and made it.More news: Boeing 737 MAX timetable uncertain as regulators continue safety review
Na and Cantlay - tied on 23 under at the end of the final day - both birdied the first additional hole, meaning they had to play the 18th for a third time. Defending champion Bryson DeChambeau and Canada's Adam Hadwin tied for the low round of the day, shooting 63 to finish tied with Brian Stuard in fourth at 20 under.