"It's a dream come true to win at Sun City and to win Africa's major", he said at the trophy presentation.
"I've got to see if I can step up to the challenge".
With a final round of 66, Grace won "Africa's Major" by a single stroke on 11 under par and ended a win drought of South Africans in this event stretching back to Trevor Immelman's triumph in 2007.
His only previous tour victory was also in South Africa, at the Nelson Mandela Championship in 2012.
His start apart, Grace believes the course suits him and hopes that his determination and comfort in the conditions will stand him in good stead.
Dubuisson moved alongside Jamieson with a four-foot birdie at the first, only for the Scot to edge back ahead by matching Grace's gain at the par-five next.
Branden Grace beat Luke Donald and Russell Knox...
He then added a fourth at the par-four 10th before making further birdies at the par-five 14th and par-three 16th; the latter a big turning point after he rolled in the 50-foot putt.
"I had to stay patient and I had to take the chances when they came my way".
There were a few nervy moments during the middle part of his round when his putter went cold and he failed to take advantage after hitting it close on several greens.
"Today I was playing, trying to get myself into some kind of contention for the tournament", he said. "It feels nice to be able to finish the day off with a good round and I'm looking forward to the next couple days".
Scott Jamieson said a win on Sunday would be the highlight of his career to date.
And Grace would love nothing more.
"This is the one event as a South African you want to win".
Dual Ryder Cup star Francesco Molinari produced the lowest round of the day with the Italian managing seven birdies in his bogey-free 65 to share fifth place on three-under par.
Sadly, the rest of the South African challenge faded on the final day, with lucky last-in-man Darren Fichardt finishing strongest of the local contingent.
Louis Oosthuizen finished tied-eighth, after a final round 70 for a four-under score, while Haydn Porteous and Charl Schwartzel were tied-12th, two-under-par, after shooting 73 and 72 respectively.