Ireland's Padraig Harrington fired an 11-under 61 on Saturday to jump into third at minus 13.
Els began the day with a one-shot lead over Lee Westwood but the South African quickly expanded the margin. He parred the first four holes but birdied the par-4 5th which turned out to be the first of six consecutive birdies. Els chipped in for birdie at the par-3 7th and nearly holed an eagle putt at 10 before tapping in for birdie.
The defending champion birdied the par-5 14th for the third straight day but ran into the only trouble of the round at the closing hole of The Gary Player Country Club. Els played his approach into a greenside bunker and blasted out to 25 feet. He missed the putt for his lone blemish of the round and a three-shot lead as he attempts to win an unprecedented third straight title in Sun City.
'I got off to a slow start. It seemed like everyone started better than me,' said Els. 'But then I just started making birdies.'
Els was embroiled in controversy before the round as a former caddie filed a lawsuit against the two-time U.S. Open champion, claiming he is owed back wages for Els' two victories in this event.
'Of course I've known about it (the lawsuit),' said Els. 'But I take care of stuff on the course and only worry about that. I'm not going to say any more because it'll get blown out of proportion so I'll rather say nothing.'
Harrington's 61 was an unofficial course record because of preferred lies on Saturday. He carded 12 birdies to only one bogey and saved par at the 9th even though his approach found water.
'After the 62 I made in the pro-am, there were a lot of expectations on me,' said Harrington, a two-time European Ryder Cupper. 'But I was more relaxed today. I was in a very aggressive frame of mind. I kept going for the flags, hitting it pin high and holing putts. I played well, but you have to have things go for you when you shoot 61.'
Westwood posted a 2-under 70 and is tied for fourth with Canadian Mike Weir. The duo stands five shots out at 12-under-par.
Sergio Garcia is the only other player in striking distance in sixth place. The young Spaniard is at 11-under after a third-round 66.
Colin Montgomerie and Nick Price share seventh at 7-under-par while reigning U.S. Open champion Retief Goosen is a shot further at minus 6.
Thomas Bjorn is in 10th at 5-under while Darren Clarke is in last at 1-over-par.
Jim Furyk was disqualified before the round started for signing an incorrect scorecard after Thursday's opening round. He misinterpreted the ruling on preferred lies.
'It was my responsibility to read the rule sheet clearly,' Furyk said. 'The paragraph relating to this rule was worded in the same way as the US Tour rule - except the last sentence.'