"I think one-under is still a good score here", he said. The victory is the eighth of his European Tour career and first since the Qatar Masters early previous year; an emotional win in the tournament styled as "Africa's major".
Dubuisson's round was a mix of four birdies and one fewer bogey as he kept alive a goal of a third Tour victory after his pair of Turkish Airlines Open wins in 2013 and 2015.
The 33-year-old Scot got up and down from through the back of the green at the last to secure second place on his own, earning a career-best pay-day of around £630,000 in the process.
Day two at the challenging Gary Player Country Club provided an even sterner test, with the players forced to overcome strong winds and a two-hour storm delay.
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.
Last year, Sweden's Alex Noren came from a similar shot deficit to win "Africa's Major" and Fleetwood will need to do the same.
"It's a very special week, we found out on Wednesday we're having a boy". "I've played with some of the best players in the world this week and proved that I can compete so hopefully I can take something out of that".
China's Li Haotong finished fourth after making eight birdies in a blemish-free round of 64 - the lowest of the week - for a score of seven-under par.
"Today I was playing, trying to get myself into some kind of contention for the tournament", he said.
"I knew I had to stay patient and take the chances when they came my way, but the key one was 16".
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.
The Englishman heads to DP World Tour Championship as firm favourite to triumph, with only Justin Rose and Sergio Garcia able to overhaul him.
Cape Town - England's Jordan Smith has withdrawn from the Nedbank Golf Challenge, hosted by Gary Player, following the second round on Friday. That put Fleetwood, who struggled on the first two days, into a tie for seventh at 2 under, six behind leader Jamieson. "(It) just gets magnified towards the end of it".
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