Having started the final day two clear of the field, but with 36 holes still to play after persistant weather problems, Els was initially overhauled by Retief Goosen in the third round, but fought back to lead by two with eight to play.
The three-time Major champion birdied the ninth and tenth holes of his final round to move to 22 under for the week, having shot a five under 67 in the morning.
Two-time US Open Champion Goosen also birdied the tenth to remain within striking distance, but there were another two shots back to Open Championship winner Louis Oosthuizen in third.
Goosen's front nine 31 in the third round had put him three ahead when else carded three bogeys in a level par 36, but Els was four shots better on the way in, and his outward 34 in the final round was one better than Goosen to extend his lead.
Further rain this morning had made the par three fourth unplayable, so the top 50 and ties who made the cut for the final 36 holes were given a nominal par there.