BANGKOK, 14 Dec 2014 (AFP) - It was the second time Westwood has won the trophy, having notched a wire-to-wire-victory at the Amata Spring Country Club course in 2011.
The tournament turned into a dramatic three-way battle on the back nine between Westwood and two players in the final group behind him, overnight leader Marcus Fraser of Australia and Germany’s Martin Kaymer.
It was a hugely frustrating day for Fraser who played steadily for a round of 70, and led or was joint leader the entire time until dropping a shot at the final hole.
In a nail-biting finish, Westwood had to watch from the clubhouse as Kaymer, who shot 68, was unable to sink the birdie he needed at the 18th to force a play-off and then Fraser missed his par putt, handing the Englishman victory with a total eight-under-par.
England's Tommy Fleetwood took fourth place, five-under for the tournament with Australia's Scott Hend a shot behind.
Local hero Thongchai Jaidee fired a 68 to join Jonathan Moore of the USA and India's Anirban Lahiri in sixth place.
Westwood's victory was all he more spectacular given that he bogeyed the first two holes.
But he pulled himself together with four straight birdies at the end of the front nine and went on to record an impressive seven birdies in all.
"I didn't get off to the best of starts and gave myself an awful lot to do," he said. "I knew I had to refocus and gave myself a talking to.
"I found my swing at the sixth and after that I really got going with four straight birdies."
The Ryder Cup star said the Amata Spring course was a real challenge.
"It is by far the hardest golf course I've played on in Asia. The greens were firm and the rough was really thick."
Fraser remained upbeat, despite his obvious disappointment at letting the lead slip at the end. His runner-up spot meant he secured one of the four places this event was offering for The Open next July at St Andrews.
"I'm really excited with getting the place at St Andrews," Fraser said. "That was one of the reasons I came to this event. The Open is the best tournament in the world."
Also clinching spots at The Open were Australia's Scott Hend, Moore and Lahiri.
"It's always something I have dreamed about," said Lahiri.
Moore said he hadn’t imagined he would get a chance to play in the Open next year.
"It's incredible," he said. "St Andrews is my favourite course."
Defending champion Sergio Garcia finished in ninth place after shooting a final round 69 which included seven birdies on the back nine.
Two-times Masters champion, Bubba Watson also hit 69, his best round of a poor tournament by his standards, but it was a case of too little too late as he finished well down the field.
Lahiri's joint sixth place meant the Asian Tour's Order of Merit this year went to American, David Lipsky who cannot be caught with just one tournament to go.
Leading scores after the final round of the $1 million Thailand Golf Championship at Amata Spring Country Club on Sunday.
280 - Lee Westwood (ENG) 70-71-72-67
281 - Marcus Fraser (AUS) 69-72-70-70, Martin Kaymer (GER) 71-72-70-68
283 - Tommy Fleetwood (ENG) 71-69-73-70
284 - Scott Hend (AUS) 70-74-71-69
285 - Thongchai Jaidee (THA) 72-71-74-68, Jonathan Moore (USA) 71-71-72-71, Anirban Lahiri (IND) 71-73-68-73
286 - Sergio Garcia (ESP) 71-75-71-69
287 - Kiradech Aphibarnrat (THA) 76-72-71-68, Paul Peterson (USA) 71-72-75-69 , Terry Pilkadaris (AUS) 77-69-72-69
288 - Thanyakon Khrongpha (THA) 69-77-73-69, Bernd Wiesberger (AUT) 76-74-68-70, Charlie Wi (KOR) 74-72-71-71
289 - Kodai Ichihara (JPN) 78-68-72-71, Daisuke Kataoka (JPN) 74-73-71-71
Selected scores:
292 - Bubba Watson (USA) 76-70-77-69
297 - Darren Clarke (NIR) 75-75-73-74