KUALA LUMPUR, April 15, 2012 (AFP) - Oosthuizen cut a miserable figure after last week's Augusta play-off, but he was all smiles following his win over Scotland's Stephen Gallacher, who pushed him until the final holes at par-72 Kuala Lumpur Golf and Country Club.
The South African, who soared to prominence when he won the British Open two years ago, shot 66, 68, 69, 68 for a 17 under par total, enough for his first victory in Asia and his second of the season after January's Africa Open.
But most importantly, the win atones for his gut-wrenching Masters play-off defeat just one week ago to America's Bubba Watson, whose mesmerising shot from trees proved the difference on the second play-off hole.
Last year's Masters champion Charl Schwartzel was sixth, six shots back, while defending champion Matteo Manassero and former world number one Martin Kaymer were both in seventh spot.
England's Danny Willett, David Lipsy of the United States, and Spain's Rafael Cabrera-Bello shared third on 12-under-par 276.
Since Augusta, Oosthuizen has flown 10,000 miles (16,000 kilometres) across 12 time zones with his wife and children and grappled with jet lag in tropical Malaysia, where capricious weather forced storm delays on Friday and Saturday.
But he candidly admitted the Masters was still on his mind when he was asked if he felt set for a great year.
"It would have been better if I had the green jacket!" Oosthuizen said. "I had a good week last week and I'm looking forward to the next majors."
Oosthuizen had to rise early to complete seven holes of his third round, after heavy showers curtailed Saturday's play. He finished it with 69 to maintain his narrow, one-shot lead over Scottish journeyman Gallacher.
He dashed straight back out for his fourth round and, as hot sun replaced the rain-clouds, raced through the front nine with three birdies against a bogey on the par-four sixth to turn at 15 under, a lead of two shots.
Fellow South African Schwartzel, who shot a stunning 64 in round one before slipping off the pace, had got off like a shot with birdie, eagle, birdie on holes four to six, and he picked up another stroke on the 10th.
But he pretended to snap his putter in frustration after a bogey on 13 slowed his charge, and then drove into the water on 16 as his challenge dissolved.
Meanwhile Gallacher slashed Oosthuizen's lead back to one shot when he birdied the 10th, and he held his nerve with a five-foot save on the par-four 13th to keep pressure on the front-runner.
But within minutes Oosthuizen, playing the same hole in the very next group, arrowed his pitch to within eight feet and duly holed out for a two-shot cushion on 16 under par.
Oosthuizen's putter was running hot and he was in disbelief when a 30-foot birdie putt just veered centimetres (inches) left on the par-four 14th. He then shaved the cup with another long putt on the par-three 15th.
And the 29-year-old, who had won only three European Tour events before this season, finished it as a contest on 16 when he swept a stunning long iron shot from rough to within three feet to move to 17 under and a three-shot lead.
Oosthuizen was lucky to dodge a bunker as he landed in rough by the 18th green but he calmly chipped on, putted to three inches, and then waited for his partners to finish before tapping in for victory.
"I'm a little bit surprised because I thought I would be tired," he said. "I played well and the game was there so that made it a lot easier. My game was a bit up and down but I kind of settled down for the final 18 holes."
Earlier, Germany's Kaymer was four under through 10 holes but he came apart on the home stretch and finished with an ugly triple-bogey in front of massed fans on the 18th green for 71.
Six-time European Tour winner Alvaro Quiros finished tied for 29th and New Zealand major-winner Michael Campbell had to settle for a share of 63rd as his seven-year win drought continues.
Leading fourth-round scores at the Maybank Malaysian Open on Sunday (par 72):
271 - Louis Oosthuizen (RSA) 66-68-69-68
274 - Stephen Gallacher (SCO) 67-68-69-70
276 - Danny Willett (ENG) 69-69-67-71, David Lipsky (USA) 70-67-69-70, Rafael Cabrera-Bello (ESP) 67-72-66-71
277 - Charl Schwartzel (RSA) 64-75-70-68
279 - Martin Kaymer (GER) 70-67-71-71, Hennie Otto (RSA) 71-64-72-72, Romain Wattel (FRA) 68-68-72-71, Matteo Manassero (ITA) 70-72-68-69
280 - Jeev Milkha Singh (IND) 65-73-70-72, Jbe Kruger (RSA) 70-65-77-68, Jyoti Randhawa (IND) 66-72-68-74, Victor Dubuisson (FRA) 72-68-69-71, Scott Hend (AUS) 70-71-73-66
281 - Ben Fox (USA) 70-68-70-73, Soren Kjeldsen (DEN) 68-72-71-70 Mo Joong-Kyung (KOR) 71-71-70-69, Rikard Karlberg (SWE) 73-69-71-68
Selected:
284 - Alvaro Quiros (ESP) 72-68-73-71
292 - Michael Campbell (NZL) 72-71-71-78