The victory came one week and more than 9,900 miles from a loss in a sudden-death playoff to Bubba Watson at the Masters. Oosthuizen had to make a 30-hour plane flight from the United States before beginning the Malaysian Open.
But his play was solid throughout with all four rounds in Kuala Lumpur better than 70. He had a final-round of 4-under-par 68 for a tournament total of 17-under 271. Stephen Gallacher was second at 14-under after a final round of 2-under 70.
Rafael Cabrera-Bello, Davis Lipsky and Danny Willett tied for third at 12-under.
"I thought I was going to be a lot more tired," Oosthuizen said after Sunday's win. "It was a long journey to get here and I have to be honest and say that I didn't expect to play this well because of the tiredness.
"The one thing I did know was that the game was there so that helped a lot. I was pretty tired at points in those first couple of rounds but overall it has been great and I am over the moon with the result."
Weather pushed back play since a lightning storm Friday and Oosthuizen had to play nearly half of his third round Sunday before starting his final round. He had one bogey -- at the par-4, 420 yard sixth, where he was 3-over for the tournament -- against five birdies in the fourth round.