Van Zyl, 36, stormed into a seven-shot lead just after the turn but found water twice on the back nine to record his first two bogeys of the week.
He is well-placed for a tilt at a first European Tour title but with Rory McIlroy and former U.S. Open champion Graeme McDowell both lurking in the top 10, he knows he will have his work cut out.
"It's a field of quality players," Van Zyl told the European Tour website.
"To be in this position is really an honour, and hopefully we can stay in the mix until the last nine holes on Sunday."
Van Zyl's 14 under par total equalled the 36-hole course record set by Ian Poulter last year.
Fabrizio Zanotti of Paraguay and Frenchman Victor Dubuisson share fourth place, one shot further back.
Britain's Lee Westwood, second overnight, dropped six places after a 71.
(Writing by Steve Tongue/Mark Meadows; Editing by Rex Gowar and Toby Davis)
Share
