Van Rensburg shot a seven-under-par 65 in the first round at the Houghton Golf Club, leaving Ernie Els two shots back after a 67.
Van Rensburg, who finished third in this event two years ago, decided not to take any time off over the festive season. He was rewarded by making only one bogey yesterday in a round which included six birdies and an eagle.
"I've been working really hard on my swing and it's paying off now," he said.
He narrowly missed out on his European Tour card at the final stage of the tour's qualifying school late last year, after an unpleasant round with America's Mac O'Grady, a former coach of Seve Ballesteros.
"I played with O'Grady and he made it impossible for me to play well. He accused me of walking across his line and generally being a difficult player. I'm not trying to get back at him, but I've never been given the opportunity to answer his accusation," he said.
Els, twice a US Open champion, carded 67 despite an argument with a photographer, which led to a double bogey at the par-four second hole.
Nick Faldo did not get the start to the season he had hoped for. The 41-year-old former world No 1, who is seeking points to qualify automatically for this year's European Ryder Cup team, dropped a shot at the last for a frustrating five-over 77. Asked if he was surprised that he had played so badly, Faldo replied: "There are no surprises anymore, just disappointments."
The Dutchman Rolf Muntz and Richard Kaplan, of South Africa, both ended the round on four-under 68 to share third place. Retief Goosen, a member of South Africa's double Alfred Dunhill Cup-winning team, withdrew from the event after the first round.
Tournament officials said Goosen has a fractured left arm, the legacy of a skiing accident in Switzerland over Christmas, and it has not healed enough for him to continue. Goosen managed to complete a round of 73 before he pulled out.
Justin Rose failed to make any inroads in his native South Africa and is in serious jeopardy of missing the cut after shooting a six-over-par 78.
Ireland's Paul McGinley and John McHenry also struggled on the first day, settling for five-over 77s.Reuse content