In doing so they stopped Fiji backing up its win in last week's Hong Kong sevens and becoming the first team to win the Singapore title in consecutive seasons. Whether or not they are able to hold to become series champions for the first time, Team USA are all but guaranteed a top-four spot, which would mean automatic qualification for the 2020 Summer Olympics.
South Africa staged an incredible comeback to beat Fiji 20-19 in the cup final and win the HSBC Singapore Sevens leg.
Barring any upset in Fiji's cup quarter-final match, they are likely to meet Australia or England in Semi-final.
Tiffany Faaee blazies trail in USA rugby 02:10 South Africa remains fourth in the World Series standings but closes the gap on New Zealand in third place after the All Blacks Sevens were defeated by Fiji in Sunday's quarterfinals before going down to Samoa in the 5th place playoff.
The series looks set to be fought out between leaders the United States and Fiji, who have closed to within three points.
Later on Sunday, the South Africans will take on the U.S. in a semifinal match at 9:50am, while with the other last-four encounter will be contested between Fiji and England. "It happened, and the win came because we executed the plan".
Fiji took a strong lead into the break thanks to tries from Aminiasi Tuimaba, Napolioni Bolaca and Vilimoni Botitu.
"South Africa head coach Neil Powell said he was "thrilled" with the fightback which was "reward" for the effort his players put in over the weekend".
This was before tries by Kurt-Lee Arendse, Angelo Davids and Ryan Oosthuizen injected hope into a beleaguered South African side.
Fiji lost a man to a yellow card for a tackle after the try had been scored in a major boost to South Africa's cause. But a penalty for offside gave South Africa a last chance and Selvyn Davids slotted the winning penalty.
"It was very much an up-and-down game for us, I think in that first half it was just the mistakes that we made on our ball".
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