The Welshman nailed a clutch putt on the Amata Spring Country Club’s signature 17th hole, which features a floating island green, just when it looked like his lead was there for the taking.
Donaldson went hard at the hole with his putt on the par-three, the ball bounced up for a heart beat … and then it disappeared, as did the hopes of unheralded Frenchman Clement Sordet and two-time winner Lee Westwood who had clawed back Donaldson’s lead with birdies to his bogey at the previous hole.
That pair finished tied for second at 18-under par after final rounds of five-under 67 for Westwood and two-under 70 for Sordet.
“It’s been a awesome event,” said the 40-year-old Donaldson. “The weather’s probably been the hardest thing to deal with as it’s been so hot all week. But I’ve had a great week. It’s an awesome tournament.
“It was a good job that putt on 17 was on line as if hadn’t gone in, it would have been in the drink. But it was right at the middle of the hole all the way. I just had to hope it would stay in and it did.
“I hadn’t played great this year so it was important to come here and work hard and kick on from there. That’s as well as I can play and I’m really happy.”
The victory – the eighth of Donaldson’s career – also secured him one of four places that were up for grabs at The 145th Open Championship, to be palyed next July at Royal Troon.
He’ll now be joined there by Sordet, Westwood and 16-year-old Thai sensation Phachara Khongwatmai, who finished Sunday alone in sixth-place at 13-under, one place behind world number 12 Sergio Garcia and European Tour Rookie of the Year An Byeong-hun who both finished on 14-under and who were already exempt for The Open.
World number four Bubba Watson, the top-ranked player in the field, produced a magic moment when acing the fifth – and the American said it would be a memory he would always cherish as he fired home a five-under 67 to finish the tournament on eight-under-par.
“It made the week pretty special,” said the American. “It was my fifth hole-in-one but the first time in competition so obviously it was nice. It got the round going. I just wish I could have held it together for a top-10 finish. But all in all it was a good day.”
For overnight leader Sorbet, who came into the Thailand Golf Championship ranked 481 – a number that will shorten considerable once the world rankings are updated Monday – the final day was lesson in what it takes to win an event packed full of the world’s best players.
The 23-year-old Frenchman had blitzed the course on Saturday but couldn’t find the same touch Sunday.
“It’s been an incredible first six months as a professional and great to end the year with a spot secured for The Open next year,” said Sorbet, who received the championship’s final invitation.
“I didn’t expect this. I am very happy to get an invite for this tournament. It has been a great week. It’s going to be my debut appearance in a major and I think I am just going to enjoy every moment of it.”
Westwood has an affinity with the Amata Spring layout, having lifted the trophy in 2011 and again last year. The Englishman had turned for home Sunday morning three stroke off the lead and was unable to reel in Donaldson over the back nine, despite an approach shot for his birdie on the 16th that his rival later claimed to be “one of the best shots you’ll ever see in golf.”
Still, the 42-year-old was looking to the future and the fact he too will be lining up at The Open once again.
“It’s great to be have made it into The Open,” he said. “I’ve played every one since 1995 so it’s great to keep that run going. It’s been 21 years now and I’ve not missed one, so I’m happy. I’ve played Troon quite a few times, finished fourth one year  so that was pretty good. I like the golf course. It’s a traditional links course – straight out straight back and everything you want from a links course.”
Teenage sensation Phachara had the local galleries roaring their approval all day as he shot a final-round six-under 66. He’d won his way into the field via last Monday’s qualifying round – and said he simply could not believe his luck.
“I didn’t expect myself to play so good,” said the Thai player. “I was already very happy just to get a chance to play with the top stars this week. I surprised even myself to finish so well.
“I played with no expectations so I guess that was the key to playing well today. I am overwhelmed with happiness that I can be able to be included in The Open next year.”
About the Thailand Golf Championship
Organized by Gulf Sports Management and IMG, and sanctioned by the Asian Tour, the fifth edition of the Thailand Golf Championship will be staged at the award-winning Amata Spring Country Club in Chonburi between 10-13 December. The Championship, the Asian Tour’s season-ending event, has a total prize purse of US$1 million, and has been part of the Open Qualifying Series since 2014. The Thailand Golf Championship will be broadcast globally by Asian Tour Media and in Thailand by TrueVisions.
Former winners of the Championship are: Lee Westwood (2011), Charl Schwartzel (2012), Sergio Garcia (2013) and Lee Westwood (2014).