Jamieson had held a five-stroke advantage after 54 holes but seven birdies from 2010 Open champion Oosthuizen gave him a sixth European Tour win on 16-under 272 ahead of Briton Jamieson (72), who nearly holed a chip at the 18th to force a play-off.
Thailand's Thongchai Jaidee (68) sealed third place a shot further back while triple Major winner Padraig Harrington (68) finished fourth on 12-under.
Oosthuizen, who yesterday surrendered the lead as he struggled to a 74, birdied two of the first three holes to put the pressure on Jamieson.
Further birdies at the sixth and eighth holes rounded off an outward nine of 32 and he had reduced the deficit to one by the turn.
Birdies at the 10th and 11th holes propelled him into the lead, and despite bogeying the par-four 16th after finding the greenside bunker, Oosthuizen's two-putt pars at the 17th and 18th holes were enough to clinch victory.
"I played the complete opposite of what I did yesterday," the 30-year-old, who will move to a career-high fourth place in the rankings released on Monday, said.
"Yesterday I felt really uncomfortable - my swing felt long and unstable. This morning I worked on a few things on the range and put my head down. I knew if I could just put a score up there, or just get close to Scott, that I had a good chance."
Oosthuizen, who has now recorded a win in the last three seasons in his native South Africa, said his ambition was to climb even higher in the rankings although world number one Rory McIlroy was a little far off.
"Top spot is a tough one. I think Rory (McIlroy) is far ahead, so if I can somehow get myself to number two then I can work on trying to get to number one," he said.
Scot Jamieson, who won his maiden European Tour title at the inaugural Nelson Mandela Championship in Durban five weeks ago, nearly forced a play-off when his eagle chip at the short par-four 18th finished inches from the cup.
"I almost had a grand-stand finish at the end there," the world number 100 said after a frustrating day where he managed just three birdies, a double-bogey on the front nine proving costly.
"I just couldn't make any birdies after doubling the fifth. That was just a bit of a kick in the teeth. I had a ton of chances and just couldn't take them."
Following his play-off triumph in December at the rain-shortened 36-hole event, Jamieson said he found it more difficult this time around with a significant advantage going into the final round.
"It's a completely different mindset, but you try and make it as similar as possible. But it's a lot easier to get yourself up for it when you're trying to chase somebody," said the 29-year-old.
"If you have a healthy advantage it's difficult to raise yourself to think that you need to make birdie - because you don't necessarily do," added the European Tour Race to Dubai money leader before paying tribute to Oosthuizen.
"Louis is a great player, and a major champion, so there's no shame in losing to him. I gave it my all - it just wasn't to be today."
Four-times major winner Ernie Els finished with a two-under 70 to end on seven-under 281, a shot ahead of fellow South African and twice US Open champion Retief Goosen (70) who was making his comeback after a five-month injury lay-off.
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