Scott was two further back after five birdies in his first 11 holes, while American Phil Mickelson eagled the first two par fives he came to, the third and seventh, to sit third on ten under.Last week’s BMW Masters winner Peter Hanson, needing a win to dislodge Rory McIlroy at the top of The Race to Dubai, turned in a three under par 33 to share fourth with Ireland’s Shane Lowry and American Scott Piercy.
Oosthuizen picked up further shots with six feet putts at the 15th and 16th and took him four clear of Mickelson.
With Scott having back-to-back bogeys at the 12th and 13th, the four-time Major winner moved into second place on 12 under with birdies at the ninth and 12th.
Two closing pars gave 30 year old Oosthuizen a course record 63 - and a five stroke lead when Mickelson missed a four foot par putt at the 14th.
Scott had come back from his two bogeys with two successive birdies, but he failed to get up and down from short of the 17th and so was alongside Mickelson on 11 under.
A brilliant approach to two feet on the 12th gave Els his eighth birdie and with Lowry closing with a 15 foot putt on the long ninth for a 68 they were joint fourth on ten under, but Hanson was two further back after a chip came back to him and he double-bogeyed the 12th.