Els completed the event at 24-under-par 264, which was a new tournament record. Tony Johnstone set the old mark of 267 in 1993. Els last won in 2005 at the Alfred Dunhill Championship. He has won at least one worldwide title every year dating back to 1992.
'There were a lot of different emotions going on today,' admitted Els. 'I view the South African Open like I do a major, and that's how I played this week.'
Third-round leader Trevor Immelman, a two-time winner of this event, closed with a 1-under 71. He took second place at 21-under-par 267. Patrik Sjoland and Els were the only two players with four rounds in the 60s. Sjoland posted a Sunday 67 to finish third at minus-20.
After nearly perfect scoring conditions during the third round, Sunday's final round at Humewood Golf Club saw some rain and the wind pick up -- as it gusted up to 25 m.p.h.
Els made his move early in the round. He stuck his second shot at the par-4 second within 5 feet and knocked the birdie putt in the hole.
After a pair of pars, Els left himself tap-in birdie putts at five and six to move to 20-under. The turning point of the round was the sixth as Immelman could not save par from a greenside bunker to fall one behind his countryman.
Els cruised around the turn with five straight pars. Immelman slid two back with a bogey on the eighth. He reclaimed that stroke with a birdie on No. 11.
However, Els responded by converting back-to-back birdies from the 12th to extend his lead to three strokes. Immelman matched Els' birdie at 15, but Els was not done.
The eighth-ranked player in the world birdied the 16th, to post five-under on that par-5 this week. Els made it three straight as he birdied 17. Immelman matched that birdie, but was four back.
Els tripped to a bogey at the last, but it was enough for his fourth win here.
'That's as good as I can play probably,' said Els. 'Under the circumstances I was chasing the first couple of holes and then I was in the lead and then I had to protect the lead and be aggressive.'
Darren Fichardt closed with a four-under 68 to finish alone in fourth at 16-under-par 272. Retief Goosen, last year's winner, was one stroke further back after a final-round 70. Goosen was joined at minus-15 by Andrew Raitt (70) and Louis Oosthuizen (67).
Gary Lockerbie (65) and Lee Westwood (70) shared eighth at 14-under-par 274.