Els was at 12-under 204 in the 12-player tournament, which offers a first prize of $2 million ' the richest in golf.
Colin Montgomerie had the day's best score with a 65 to share second place with Chris DiMarco (72) at 208.
Darren Clarke and Retief Goosen were at 210, with Michael Campbell and Padraig Harrington a stroke behind. Jim Furyk was at 212, followed by defending champion Sergio Garcia at 213, Nick Price and Bob Estes at 214 and Robert Allenby at 215.
Els, playing in his home country, could not match his 65 from the second round. His approaches and putting were not quite as sharp.
``It looked good on the scorecard but I didn't play my best today,'' Els said. ``I got it around and just hung in there.''
Montgomerie had four consecutive birdies and an eagle on the front nine. The Scotsman shot a 74 in the first round
``No one else has played better than I have since I shot that quadruple-bogey eight on the first hole,'' Montgomerie said.
DiMarco was within one shot of Els after the first round. He had a frustrating third round after consecutive 68s. His first bogey came on the 18th on the second round, and he started his third round with two more bogeys.
Clarke shot a 71 to leave him six shots off the pace, and that may be too big a gap to close.
``But I have to carry on, giving myself the kinds of chances I have been giving myself all week, and hope the putts start sinking,'' he said. ``It will take unbelievable golf to break 65, but I had the chances to do it today.''
Full-field scores from the Nedbank Golf Challenge