JOHANNESBURG, 1 Mar 2015 (AFP) - The perpetually jovial 28-year-old fired a final-round 66 for a 270 total at Royal Johannesburg and Kensington Golf Club and a two-stroke triumph.
He won the South African Open in Johannesburg two months ago, pipping local favourite Charl Schwartzel on the first hole of a play-off.
It was a special day for Sullivan, who not only collected a 206,050-euro ($230,000) cheque, but also automatic entry to the 2015 British Open at St Andrews.
He ended a South African monopoly of the Joburg Open, too, with the last five winners locals, and six of the eight since the championship started.
"Unbelievable," was the initial reaction of the 1.75-metre native of English midlands town Nuneaton when handed the trophy by Johannesburg mayor Parks Tau.
"I never in my wildest dreams imagined winning two South African tournaments in such a short space of time.
"What made this win particularly great was that I really enjoyed myself all week. I am on the crest of a wave.
"Thanks to my coach, my psychologist and all the other people who have helped me become a better golfer," said Sullivan, who is ranked 73 in the world.
The top three finishers in the European Tour-Sunshine Tour event secured British Open berths and the others went to Englishmen David Howell and Anthony Wall.
Howell (69) and Wall (68) tied for second place with South Africans Wallie Coetsee (71) and Jaco van Zyl (66) and Irishman Kevin Phelan (66), but secured the spots on a world-rankings tie-breaker.
Sullivan laid his victory foundations on the outward nine, picking up five birdies and not dropping a shot in partly cloudy conditions that gradually grew gloomier.
He had a blip by bogeying the par-four 11th, but recovered to collect two more birdies on the final four holes.
Leading Joburg Open final-round scores Sunday at the par-72, 6345 metres-6940 yards Royal Johannesburg and Kensington Golf Club east course (RSA unless noted):
270 - Andy Sullivan (ENG) 71-65-68-66
272 - Wallie Coetsee 66-65-70-71, David Howell (ENG) 66-69-68-69, Kevin Phelan (IRL) 67-68-71-66, Anthony Wall (ENG) 67-66-71-68, Jaco van Zyl 69-67-70-66
273 - Byeong Hun An (KOR) 65-72-70-66, Jacques Blaauw 67-69-67-70, Chris Swanepoel 70-67-67-69
274 - Thomas Aiken 67-67-70-70, Kristoffer Broberg (SWE) 67-67-72-68, Adrian Otaegui (ESP) 71-68-69-66
275 - Dean Burmester 64-73-73-65, Anthony Michael 68-67-69-71, Callum Mowat 71-65-71-68, Garth Mulroy 64-68-72-71, Paul Waring (ENG) 68-69-67-71