DURBAN, January 12, 2014 (AFP) - Oosthuizen started the day in fourth place, two shots adrift of overnight leader Tommy Fleetwood, but an eagle at the eighth at the Durban Country Club got him into contention.
He then birdied four of the last six holes to finish a shot clear of compatriot Branden Grace and two ahead of Dutchman Joost Luiten and Fleetwood.
The Englishman was undone by three bogeys in five holes on the front nine.
Oosthuizen, the 2010 British Open champion, has now won on the European Tour in five successive seasons and has started the season with a win on home soil for the fourth year running.
"It means a lot. There's something about this golf course that I love. It's great in front of the home crowd to get my first win of the season and hopefully I can build on this and get a few more," he said.
"I felt really comfortable today, especially on the back nine. Once I stood over my second on 17, I saw Branden had made birdie on 18 and I knew it was crucial for me to get within 10 feet to give myself a proper birdie opportunity and I hit it really close.
"At 18, I just wanted to get it past the pin to chip back into that green. I got that right and hit a really a good shot."
He added: "It puts pressure on you defending your title but you always know that you played well last year and you just try to do the same the next year."
Grace was left to rue a first-round of 74 which left him with a lot of catching up to do, although he came mighty close after a final-day 68 which featured just one bogey.
"I thought I played some superb golf today. I let a couple slip out there which was unfortunate but if you had told me my first event I would start off with a second place, I would have taken it," he said.
Meanwhile, it was also a good day for Irishman Padraig Harrington, who has not won on the European Tour since his 2008 US PGA triumph, but who shot a 67 to finish tied fifth.
Scores after the final round of the $4 million (2.94m euros) Volvo Golf Champions event on Sunday at the Durban Country Club (GBR & IRL unless stated, par 72):
276 - Louis Oosthuizen (RSA) 68 69 71 68
277 - Branden Grace (RSA) 74 67 68 68
278 - Joost Luiten (NED) 70 67 70 71, Tommy Fleetwood 70 67 69 72
279 - Padraig Harrington 71 71 70 67, Raphael Jacquelin (FRA) 67 73 70 69, Victor Dubuisson (FRA) 69 69 69 72
281 - Thomas Aiken (RSA) 72 72 70 67, Julien Quesne (FRA) 74 73 66 68
283 - Thomas Bjorn (DEN) 79 68 67 69, Matteo Manassero (ITA) 72 67 73 71, Brett Rumford (RSA) 73 70 68 72
284 - Morten Orum Madsen (DEN) 71 74 69 70, Jamie Donaldson 71 71 68 74
285 - Marcel Siem (GER) 70 71 72 72, Miguel Angel Jimenez (ESP) 76 70 67 72, Charl Schwartzel (RSA) 74 69 68 74
286 - Chris Wood 70 71 71 74
287 - Gonzalo Fernandez Castano (ESP) 74 73 71 69, Mikko Ilonen (FIN) 73 73 69 72, Paul Casey 72 75 65 75
288 - David Lynn 71 74 72 71, Jin Jeong (KOR) 73 76 68 71
289 - Kiradech Aphibarnrat (THA) 75 74 71 69, David Howell 76 69 71 73, Colin Montgomerie 70 74 69 76, Darren Clarke 69 71 72 77
291 - Richard Sterne (RSA) 72 73 73 73
292 - Stephen Gallacher 73 74 72 73, Michael Hoey 72 73 73 74
293 - Simon Thornton 70 72 80 71
294 - Robert Karlsson 74 72 73 75
295 - Dawie Van der Walt (RSA) 71 71 75 78
296 - Peter Uihlein (USA) 70 78 70 78
297 - Darren Fichardt (RSA) 73 71 74 79
300 - Jose Maria Olazabal (ESP) 73 77 77 73