The 30-year-old returned to the Sentosa Golf Club early yesterday morning to complete the last ten holes of his final round after thunderstorms caused a five-and-a-half-hour suspension of play on Sunday.
The Australian resumed with a comfortable three-stroke lead over the rest of the field but saw that disappear with dropped shots on the 10th and 14th holes. However, he fought back in his closing four holes with two birdies - including a fine putt from 10 feet on the 18th - to finish with a three-under-68 and become the first player to win the tournament on three occasions following previous wins in 2005 and 2006. "It's a new experience for me as it's the first time I've won three times.
"I'm very proud to win the National Open and these are the kind of events that you dream of winning when you're growing up as a kid," said Scott, who rises from 41 to 20 in the new world rankings.
"I haven't been putting my best lately and the demons started creeping in a little bit on the back nine. But fortunately I squashed them and made a good putt on 15. That gave me a little buffer and calmed me down for the last three."
The win was Scott's seventh on the European Tour and first since winning the Qatar Masters in 2008. "It feels great. It's a relief to finally get finished," added the former world No 3. "It's been a long week and it was a bit of a grind this morning. It's not an easy back nine to come out and play and I didn't make it look that easy either, so I'm just happy to be done and be the winner again."
Denmark's Anders Hansen shot a 68 to finish second - three shots behind Scott - although he could have threatened a closer finish had he holed a birdie putt on the 15th.
"I thought if I had holed that one I would only be one behind with three to go and then you never know. But I missed it so the chance was gone," he said.
"Adam is a great player and he thoroughly deserves his victory."
Graeme McDowell posted a one-under 70 for a share of third place with Sweden's Rikard Karlberg (67) to boost his chances in the Race to Dubai.
With current leader Martin Kaymer only managing to finish 10th, McDowell cut the German's advantage on the European Tour's money list and the Northern Irishman has the chance to gain further ground at the UBS Hong Kong Open this week.
Last year's champion Ian Poulter saw his challenge fade away with a disappointing 73 to leave him in a tie for sixth place - six shots adrift of the winner. Top Scot was David Drysdale in joint 21st, with Colin Montgomerie one shot behind after finishing with a 71. Alastair Forsyth, Richie Ramsay and Paul Lawrie had all missed the cut.