Jeju - Justin Thomas won the CJ Cup on Sunday for the second time in three years, but it took until the closing stretch to see off the dogged challenge of Danny Lee on South Korea's Jeju Island.
The pair, who shared a three-shot overnight lead on 15-under par were locked together until the short par-four 14th.
"I felt like 14 was a pretty big change in momentum," said Thomas, who got up and down from 65 yards for a crucial birdie, and from that moment was never headed as he finished with a round of 67 and a 20-under par total of 268.
"Danny made it extremely difficult. I kept trying to hit fairways and greens and give myself a lot of birdie chances, and he just kept getting up and down from everywhere," said world No 5 Thomas, who pocketed $1.755 million for the win.
Seoul-born New Zealander Lee, who started the day tied for the lead at 15-under par with Thomas, carded a three-under par 69, cheered on by huge galleries hoping for a first Korean-born winner of the PGA Tour event.
There was a three-way tie for third on 15-under par between Japan's Hideki Matsuyama (65), US Open champion Gary Woodland (66) and Australia's Cameron Smith who finished with an eagle for a 69.
But none of them remotely threatened the leading pair who fought out a compelling head-to-head shootout in perfect conditions under clear blue skies.
American Thomas, from Louisville, Kentucky, has been watched all week by his parents, who flew over to support him.
"My dad turned 60 last week, so maybe it's a little 60th birthday gift to him. I'm glad he didn't come over here to watch me not play very well," said Thomas, who won the inaugural 2017 CJ Cup at the spectacular Nine Bridges club, set on the slopes of South Korea's tallest mountain, Hallasan.
Thomas has now equalled Jordan Spieth and Rory McIlroy by winning 11 PGA Tour titles before his 27th birthday.
Only Tiger Woods and Jack Nicklaus had won more by that age, and four of Thomas' wins have come from just nine PGA Tour starts Asia - he won the CIMB Classic in Malaysia in 2015 and 2016.
"It's always nice playing, trying to win in a place you've already won at," said Thomas.
"I've only had that opportunity one other time in Malaysia, but it's pretty awesome. I don't know, something about Asia I like."
World No 162 Lee eventually blinked first under relentless pressure with bogeys at 15 and 16.
But there was still time for one last twist as Thomas' par putt on the short 17th lipped out and he went to the 18th two shots up.
There had been a three-stroke swing on the 18th on Saturday when Lee holed a snaky 60-foot eagle putt while Thomas dropped a shot after finding water.
This time Thomas stayed dry, though Lee came within a whisker of repeating his eagle of the previous day - but this time the long putt horseshoed out and a relieved Thomas was left with two putts for the title. He needed only one.
"Before I teed off my very first tee shot on Thursday, if someone's going to give me solo second, I would take it in a heartbeat," said Lee.
Final scores on Sunday after the final round of the PGA Tour's CJ Cup at The Club at Nine Bridges Golf Club, Jeju Island, South Korea (par 72):
268 - Justin Thomas (USA) 68-63-70-67
270 - Danny Lee (NZL) 67-66-68-69
273 - Hideki Matsuyama (JPN) 69-70-69-65, Gary Woodland (USA) 71-71-65-66, Cameron Smith (AUS) 67-69-68-69
275 - Tyrrell Hatton (ENG) 69-68-70-68, An Byeong-hun (KOR) 64-69-73-69
276 - Ryan Moore (USA) 69-67-72-68, Kiradech Aphibarnrat (THA) 69-69-69-69, Wyndham Clark (USA) 71-67-67-71, Jordan Spieth (USA) 70-65-70-71
277 - Corey Conners (CAN) 70-72-69-66, Ryan Palmer (USA) 70-69-70-68, Joaquin Niemann (CHI) 65-73-71-68, Kevin Streelman (USA) 69-69-69-70
278 - K.J. Choi (KOR) 69-74-68-67, Jhonattan Vegas (VEN) 73-70-72-63, Graeme McDowell (NIR) 68-71-68-71, Ian Poulter (ENG) 69-72-66-71
279 - Tommy Fleetwood (ENG) 71-70-71-67, Andrew Putnam (USA) 70-70-71-68, Matt Jones (AUS) 72-70-72-65, Nate Lashley (USA) 72-69-70-68, Kevin Na (USA) 72-68-70-69, Charles Howell III (USA) 67-70-72-70
280 - Kang Sung-hoon (KOR) 72-72-68-68, Kim Si-woo (KOR) 69-68-74-69, Harold Varner III (USA) 71-71-68-70, Rafa Cabrera-Bello (ESP) 68-74-68-70, Emiliano Grillo (ARG) 69-66-72-73
281 - Viktor Hovland (NOR) 69-69-74-69, Phil Mickelson (USA) 70-72-71-68, Pat Perez (USA) 73-69-70-69, Jason Day (AUS) 66-73-71-71, Rory Sabbatini (SVK) 71-69-69-72
282 - Charley Hoffman (USA) 67-72-73-70, Hwang Jung-gon (KOR) 67-71-74-70, Collin Morikawa (USA) 69-73-65-75
283 - Lee Soo-min (KOR) 68-72-73-70, Lucas Glover (USA) 74-69-71-69, Im Sung-jae (KOR) 68-73-70-72, Lee Kyoung-hoon (KOR) 69-67-72-75
284 - Marc Leishman (AUS) 72-69-72-71, Dylan Frittelli (RSA) 70-70-71-73, Joel Dahmen (USA) 74-71-70-69
285 - Adam Schenk (USA) 71-74-67-73, Lee Hyung-joon (KOR) 71-71-71-72, Kevin Tway (USA) 70-72-71-72, Branden Grace (RSA) 71-71-70-73, Keith Mitchell (USA) 74-72-68-71, Chase Koepka (USA) 70-72-73-70, Adam Long (USA) 73-72-70-70, Chez Reavie (USA) 68-77-70-70, Danny Willett (ENG) 76-71-70-68, Moon Kyong-jun (KOR) 76-72-71-66
286 - C.T. Pan (TPE) 74-69-72-71
287 - Luke List (USA) 70-75-71-71, Troy Merritt (USA) 74-72-70-71, Abraham Ancer (MEX) 73-74-71-69
288 - Sergio Garcia (ESP) 73-70-72-73, Park Sang-hyun (KOR) 74-68-74-72, Vaughn Taylor (USA) 74-71-71-72
289 - Chesson Hadley (USA) 75-76-72-66
290 - Billy Horschel (USA) 71-74-76-69
291 - Jazz Janewattananond (THA) 74-74-70-73, Max Homa (USA) 69-82-69-71
293 - Ham Jung-woo (KOR) 74-72-73-74, Won-joon Lee (AUS) 74-73-79-67
294 - Michael Kim (USA) 76-72-71-75, Whee Kim (KOR) 76-75-70-73, Bae Yong-jun (KOR) 78-72-73-71
296 - Brian Stuard (USA) 72-76-75-73, Chang Yi-keun (KOR) 73-73-80-70
299 - Matthew Wolff (USA) 73-78-78-70
301 - Scott Piercy (USA) 72-72-79-78
307 - Lee Tae-hee (KOR) 74-77-77-79
Withdrawn: J.B. Holmes (USA), Brooks Koepka (USA)