Ormsby overcame a disastrous triple bogey on the third hole to shoot a final round one-under-par 71 to win the US$300,000 tournament by one stroke from the 56-year-old Boonchu, who was bidding to become the oldest winner on the region's premier Tour.
The wire-to-wire win earned Ormsby's the winner's cheque of US$54,000 and moved him up to eighth place on the Order of Merit.
Singapore's Lam Chih Bing, who led briefly during the final round, settled for third place after carding a level par 72 while Shiv Kapur's search for a first win on his home course was extended after he bogeyed two of his last three holes to finish three shots behind Ormsby in fourth position.
Ormsby, who held at least a share of the lead from the opening day, birdied the second hole but stumbled badly with a seven at the next hole.
However, the Aussie showed great character by shooting birdies on the fifth, seventh and eighth holes to stay in the title hunt.
He bogeyed the 12th and needed an 18-foot birdie conversion on 17 which proved decisive as Boonchu's title challenge faded with a bogey on 16.
"It means so much. I've played tournaments worldwide but to finally get a win in Asia is fantastic. I felt pretty good on the fourth tee but I just put my head down and tried to get down into it and birdied the fifth," said Ormsby.
"I was so disappointed in Malaysia and Chiangmai as I played well on both weeks but didn't finish them off. I knew there was a win in there for me and I am glad I came here," added the Australian who finished tied-33rd and tied-20th in Malaysia and Chiangmai respectively.
Boonchu, who was bidding to become the oldest winner in the Asian Tour history, seemed on course to create history but a costly bogey on the 16th put paid to all hopes.
"Conditions were really tough out there the entire week but to be able to play the way I did even at 56 years old really says a lot about my game," said Boonchu.
"I've shown that I still have what it takes to compete against the younger boys but I just ran out of steam towards the end. But overall, it has been a good week and all I can say is never write off an old man!" smiled Boonchu.
Despite finishing third, Lam found the much needed self-belief again. The 36-year-old was seeking to end his five-year title drought and losing his Tour card last season was a rude awakening for him.
"Maybe losing my Tour card last year was a blessing in disguise as it was a wake-up call. I reassessed my game and took pains to put in those extra hours in getting back my best form," said Lam.
"Just being back in contention means a lot and more than anything else, I've learnt to believe in myself again" added Lam
As the top-three players at the Panasonic Open India, Ormsby, Boonchu and Lam will be extended invitations to the Asia-Pacific Panasonic Open, sanctioned by the Asian Tour and Japan Golf Tour Organisation, in Osaka, Japan in September.