"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".
Grace became the first South African in 10 years to win the tournament after Trevor Immelman triumphed here in 2007.
"This is the one event that as a South African you want to win".
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.
Stephen Gallacher's season is also now over, but Jamieson has ignited his at an exciting time after producing four polished rounds on one of the toughest courses on the European Tour circuit.
Jamieson could only manage a final-round 70 to leave the Scot in second, while Frenchman Victor Dubuisson also had a spell at the top of the leaderboard on Sunday before settling for a 70, which left him another shot adrift in third position.
"It's "Africa's Major" for a reason, and it's one of those you're going to have to play well to win".
"It's a very special week, we found out on Wednesday we're having a boy". The Glaswegian had just scraped into the penultimate Rolex Series event of the year and needed a high finish to have any chance of moving on to the final one in Dubai.
South Africa's Haydn Porteous posted a five-under 67 to be at three-under, while Race to Dubai leader Tommy Fleetwood hit back after a hard first two days to also post a 67.
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.
"I'll take that for sure", said the 33-year-old whose only win on the European Tour came in 2013 at the now-defunct Nelson Mandela Championship at Royal Durban on the east coast. "I'm sure I'll look back and take great pride in this", he said. I always play well here.
Tommy Fleetwood remains on top, with Justin Rose and Sergio Garcia the only men who can overtake him.
Cape Town - England's Jordan Smith has withdrawn from the Nedbank Golf Challenge, hosted by Gary Player, following the second round on Friday. "(It) just gets magnified towards the end of it".