With his second victory on the region's premier Tour this season, the Thai veteran also completed his royal collection having won the Queen's Cup twice in 2012 and 2014 when it was staged as an Asian Tour event.
Lahiri, who led from the opening day, had to settle for a share of second place with Australia's Andrew Dodt while Qualifying School graduate Kalem Richardson of Australia enjoyed another good outing in Thailand by taking a share of fourth place with Thailand's Donthai Boonma and Paul Paterson of United States.
Rashid Khan stormed to a fine round 66, including an eagle two on par-4 ninth. He finished tied 13th at 11-under, while first round co-leader again struggled on the greens with a round of 72 for a total of 10-under and he was tied 16th, the same as Daniel Chopra (67).
Arjun Atwal (75) was tied 54th at three-under 285 while S Chikka (72) recovered form his third round 78, to finish at one-under and in tied 63rd place.
Lahiri was visibly disappointed not to have won again as another victory at the US$500,000 event would have meant more world ranking points and allowed him to close the gap on Order of Merit leader David Lipsky of United States.
Lahiri said, "I wasn't at my best today as I was really struggling on the greens. Thaworn was magic on the greens. Off the greens, he played fantastic on the front-nine and on the back-nine I had my chances and I just didn't take them.
"I would have like to have won this week. We are not playing for lots of money and it's difficult to bridge such a big gap and I'm running out of tournaments. I've to win at least one of these next three events to have a chance at winning the Order of Merit. I'm a little upset I didn't close it out as I led wire-to-wire this week. I guess Thaworn was the better player today. I don't think I played poorly but it
was just not good enough to close it out," said Lahiri.
He added, "I just missed way too many putts and it was disappointing to miss a short one on the last and that is going to hurt my world rankings. I'm upset with that. But it's a solid week all in all and I'm happy with the way I'm playing. I just got to pick myself up and win next week."