Oosthuizen had a 72-hole total of 27-under 265, with a 17th-hole birdie Sunday clinching a two-stroke victory over Tjaart van der Walt. Retief Goosen was third at 24-under and Jaco Van Zyl finished four strokes off Oosthuizen's pace for fourth.
Van der Walt and Goosen each shot 69 in the final round while Van Zyl had a 7-under 66 on Sunday. The top four finishers are all form South Africa.
Oosthuizen opened Sunday's play with a birdie but followed that with a bogey at the par-3 second hole. However, he dropped in an eagle at the 506-yard, par 5 third hole -- a hole he was 5-under on for the week.
He had a bogey at the fifth hole but birdied three of the next four holes to make the final turn at 4-under on the day. Oosthuizen added a birdie at the 11th hole and strung together a series of pars while the rest of the field struggled for birdies to catch him.
A 2 at the par-3 17th combined with van der Walt's bogey on the hole to virtually lock up the win.
It is the fourth European Tour title for Oosthuizen, who in addition to last year's Africa Open, won the British Open and the Andalucia Open in 2010. He collected more than $200,000 along with the championship.
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