A stunning South Africa comeback prevented Fiji from claiming back-to-back World Rugby Sevens Series triumphs in Singapore Sunday.

Nineteen points down at halftime in the gold medal match, the Blitzboks rolled off three tries and a late penalty to secure a remarkable 20-19 turnaround victory.

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.

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"Going into the finals is always going to be difficult. It's natural to have a bit of doubt and disbelief," Powell said.

"I think just going to the field and telling the guys that we're still in the game and if we score first we can give ourselves a shot at winning this helped to inspire the younger players. They hung onto every word we said and started to believe it.

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.

Fiji, successful in Hong Kong last time out, remains second in the standings but is now just three points behind series leader USA.

Gareth Baber, Fiji's head coach, said injuries played their part in clipping his side's momentum. But he credited a "very good" South Africa team on its victory and pointed to the positives for Fiji over the last few weeks.

"We won Hong Kong last week. We got into another final, so we're doing something right" Baber said. "But we didn't get it all right this weekend. We had a bumpy ride but showed the resilience in the game. The group pushed all their way till obviously they were beaten by a very good South African team."

Just two events remain in the 2019 men's Sevens Series calendar.

The next stage takes place in London on May 25 and 26 before the final round in Paris one week later.