The South Africans secured qualification for the Cup quarter-finals after beating Canada earlier in the day, but they were made to sweat by the Americans at Twickenham.
The Blitzboks started off strongly, with superstar Seabelo Senatla finally getting his tournament going after not taking the field against Canada.
It was Cecil Afrika and then Dylan Sage who created the space for Senatla to canter over on the outside to open the scoring, but for the rest of the half, it was all America.
First Sage made an excellent tackle to force a knock-on by US speedster Perry Baker, and later it was Baker who had to prove that he is more than just a sprinter as he used his pace to drag down Senatla just short of the tryline in the corner.
Senatla had to show off his defensive skills as well, as Zack Test had burst through and was well on his way to scoring when he was taken down from behind by Senatla, which ensured that the Blitzboks retained their 7-0 lead at halftime.
But the moment of the match came from Afrika after the break, as he sped down the right-hand touchline and ran 60m while bumping off two US tacklers along the way to score a sensational five-pointer. Crucially, he also slotted a second difficult conversion to put SA 14-0 ahead, and that proved to be the difference in the end.
America hit back and nearly got through when Baker exploded down the left after Senatla was brought down as he tried to chase his opponent, but that man Afrika was one hand to dump Baker into touch on the SA 22.
And while sevens rugby is normally about attack, it was the defence that came to the fore again for Neil Powell’s team as Chris Dry won a breakdown penalty 10m from his own line.
USA finally broke their duck in the dying minutes through tries by Nate Augspurger and Ben Leatigaga, but it was too late to change the result as both conversions were missed.
The Blitzboks also received a boost in their unlikely quest to grab the World Sevens Series title as log-leaders Fiji were stunned 31-10 by England in their opening game.
But the Fijians are still 14 points ahead on the standings, and could still clinch the series if they end up in the Bowl competition and South African win the cup.
South Africa – Tries: Seabelo Senatla, Cecil Afrika. Conversions: Cecil Afrika (2).
USA – Tries: Nate Augspurger, Ben Leatigaga.
Original source: Afrika saves Blitzboks’ blushes