England had seen off New Zealand 12-5 in the semifinal, but proved no match for the blistering Blitzboks in the the decider, as unanswered tries from captain Philip Snyman, Seabelo Senatla and Justin Geduld ended the contest before the first half was up.
England did fight back, as captain Tom Mitchell and Dan Norton gave the scoreline a look of respectability
But, determined to avenge their defeat to England in December's Cape Town final
, this was a match South Africa never looked like losing, as Stephan Dieppenaar put the game out of reach.
With three wins from four rounds, the Blitzboks now boast the best series start since the imperious New Zealand side of 2008 and lead second-placed England by 17 points in the overall standings.
"I think it was great for the guys to come out and beat England after losing to them in the pool stages," South Africa head coach Neil Powell told reporters.
"I'm delighted with the back-to-back wins in Wellington and Sydney."
Losing out to Fiji for the past two overall titles, the Blitzboks look determined to win a first championship since 2009, having reached all four finals this season.
With six cities still to visit, including the final; at London's Twickenham in May, they have already won three times as many tournaments than in the entirety of 2015-16.
"It's incredible," reflected Senatla, named Player of the Final after a number of scintillating runs.
"The guys are just magicians, hats off to them. I am just the finisher of the moves."
Senatla was the tournament's leading try scorer with nine, and leads the series with 32. However, this was his final event of the series, as he is joining up with South African 15-a-side franchise the Stormers in the southern hemisphere's Super Rugby competition.
"Seabelo is a special player and a key player. We will definitely miss him and I hope he goes on to great things in the XVs game," Powell said of the 23-year-old, who has become the Blitzboks' record try scorer with 189 touchdowns since 2013.
Senatla is fifth on sevens' all-time try-scoring list, while England's Norton is now just five behind Kenyan Collins Injera's record of 238.
Earlier, host Australia was beaten by New Zealand 20-14 in the battle for third place.
Russia picked up the Challenge trophy, thrashing France 26-0.
Olympic champion Fiji
, bidding for a third successive world series title, had to be content with fifth.
Meanwhile, the Sydney women's final on Saturday was a surprise meeting between Canada and the US.
The Canadians followed up their shock 12-7 semifinal win over Olympic champion and host Australia to triumph 21-17.
The Americans had similarly upset Rio finalist New Zealand -- which had won the opening tournament in Dubai -- in the opening semifinal, winning 19-12.