Fiji claimed a 24-19 win against South Africa before beating New Zealand 35-19 in the Cup final of the Las Vegas Sevens.
The Blitzboks thrashed the USA 31-0 in the third-place play-off but will be bitterly disappointed not to have defended their title.
The South Africans trailed 19-0 half-time of their semi-final, with Semi Kunatani scoring a brace for Fiji and Viliame Mata intercepting a Kyle Brown pass when the Blitzboks looked set to score.
The Blitzboks hit back with three second-half tries through Cecil Afrika, Seabelo Senatla and Philip Snyman, but two yellow cards – to Frankie Horne and Brown – cost them dearly.
Fiji then cruised past New Zealand in the decider, with both finalists closing the gap on series leaders South Africa, with just seven points now separating the top three.
The Blitzboks maintain their top spot with 93 series points, with New Zealand (88) and Fiji (86) in second and third respectively as the series passes the halfway stage in Las Vegas.
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