Starting the final round three shots off the lead, the 21-year-old rookie professional birdied his opening three holes at the Sarawak Golf Club and did not look back with an outstanding outward 30. He became only the second Malaysian after S. Siva Chandhran to win on the ADT, which was launched by the Asian Tour in 2010.
England's Peter Richardsan finished runner-up after closing with a solid 67 while Filipino Charles Hong signed off with a 69 to come in third in the RM180,000 (approximately US$60,000) event, which is the 10th leg of the 2012 Schedule.
"This feels so good. It's my first win as a professional and the best score in my life. My putting was so good ... I took less than 25 putts," said De Silva, who accumulated a four-day total of five-under-par 283 and earned RM31,500 (approximately US$10,500) for his breakthrough.
The Malaysian got out of the blocks superbly with three opening birdies, firing an approach to five feet on the first hole, chipping in on the second and draining a 10-footer at the third hole. But the most important birdie putt came at the last when a 20-foot curler disappeared into the cup which sealed a memorable come-from-behind victory.
"I told myself that I needed to birdie the last to win," said De Silva. "My caddie was giving me a lot of good lines and I felt confident with the last putt.
"When I got up this morning, I somehow felt good to play and I just got off to a really good start. I was really relaxed on the back nine and I drew on my experiences of winning (12) amateur events."
The victory provided a silver lining for De Silva as he suffered the agony of missing out on an Asian Tour card at Qualifying School in January with a heart-wrenching quadruple bogey nine on the 72nd hole.
He was in position to earn his playing rights on Asia's elite circuit but he sent two shots into the water to miss out. "That was my worst experience and it took me a few months to get over it. But I think I learned a lot from that," said De Silva.
"Now that I have won my first ADT event, I'm going to try to win another tournament and try to finish in the top-three of the Order of Merit (which rewards players with Asian Tour cards for 2013)."
Overnight leader Choo Tze Huang ended with a 73 to settle for tied sixth place with countryman Quincy Quek and Malaysia's Akhmal Tarmizee.
The ADT, which was inaugurated two years' ago with five events, will stage a minimum of 12 tournaments this season. One more event will be announced shortly. From next year, all ADT events will receive Official World Golf Ranking points which will be a huge boost for the development of the game in Asia.