Soyizwapi scored a try in the dying seconds of the match - cleverly running closer to the posts - and Dewald Human duly converted to catapult their side onto the top of the podium and a well-deserved win.
Scores were tied 5-all at the break, with each side scoring a try, but when Fiji scored with three minutes left, it was left to Soyizwapi and Human to create some magic and add to the team's silverware.
For SA Sevens coach Neil Powell, it was a pleasing outing, as they achieved many of their objectives on the trip.
"We came here to work on our structure and game plan and although we won the final, it's still early days in our season and we're not yet where we want to be. Nevertheless, it was a great effort from the boys out there today," Powell said.
"It's never easy against Fiji. If you give them possession and you allow them to play, they will punish you. It's always tight against them, and there is usually only two to five points in it - today was no different and I think it was an amazing final."
Earlier in the day, the South Africans had to survive two late tries from Germany in the semi-finals of the tournament, winning 17-12.
They were leading 12-0 and later 17-7 before the home side scored a late try and only desperate defence from the South Africans prevented the Germans from getting a try that would have tied the scores and giving them a possible conversion to win.
Powell was pleased with the effort on the day.
"I can't fault the guys for the amazing character they've shown out there today. We'll never go into any tournament not hoping to be successful and while we we're not as sharp as we should be, we're still very happy with the win,” he explained.
“We knew we were going to make some mistakes as the players are still settling into their roles and responsibilities, but this has been a great way to build up to the World Series."
For Powell, strong defence was important.
“We looked after our systems well and really defended well at times. We did get it wrong at times, but that was expected. We are weeks ago from our first tournament, so mistakes were always going to be part of this showing in Germany,” he said.
On the first day, South Africa outplayed New Zealand, England and Australia to top their pool.
Fiji, who topped their pool, progressed to the final with a late score, beating New Zealand 14-12 in the other semi-final.
v Germany - Tries: James Murphy, Siviwe Soyizwapi, Stedman Gans. Conversion: Dewald Human.
v Fiji - Tries: Kurt-Lee Arendse, Siviwe Soyizwapi. Conversion: Dewald Human.