Semi Radradra scored the decisive try as defending champions Fiji set up an Olympic rugby sevens final against New Zealand at the Tokyo Stadium on Wednesday.
Fiji, running a solid defensive pattern, ran out 26-14 winners over Argentina, who had surprisingly knocked out Rio bronze medallists South Africa in the quarter-finals on Tuesday.
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New Zealand outmuscled Great Britain 29-7 in the other semi-final. The British team will play Argentina in the bronze medal match.
Sireli Maqala, with strong fends off each hand, bundled over for Fiji's opening try at a baking Tokyo Stadium, with temperatures of 33 degrees Celsius (91 Fahrenheit) and 75 percent humidity.
That was quickly followed by Meli Derenalagi, who pounced on a ball that shot out unguarded from an Argentinian ruck.
Speedster Marcos Moneta, part of the Argentina team that won gold at the Youth Olympics in 2018, scored his fifth try of the tournament after picking a good line to bring Los Pumas back into the game.
After winning the restart, Argentina moved the ball to the left, where Ignacio Mendy was on hand to dot down, a touchline conversion by Santiago Mare securing his team a 14-12 half-time lead.
But Fiji did not panic, Jiuta Wainiqolo restoring his team's lead after a smart offload that saw him sprint in from halfway.
Radradra, who has lit up the European rugby scene with Toulon, Bordeaux-Begles and current club Bristol, then settled the contest with his first touch after coming on.
Showing his X-factor value, the 15s star stepped German Schulz for a straightforward run-in against a tiring Argentina side.
New Zealand, long the dominant force in world sevens, showed all their experience from the kick-off, keeping possession from Britain for a full three minutes before Scott Curry darted over from a tryline ruck.
Britain hit back through Dan Norton, the top try-scorer on the World Rugby Sevens Series showing the Kiwi defence a clean pair of heels.
Regan Ware restored New Zealand's lead after a jinking Andrew Knewstubb had drawn Norton off his wing.
Ware crossed for his second halfway into the second period, pouncing on a clever basketball-like bouncing pass from a ground-bound Tim Mikkelson to scoot in unmolested.
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It was game over from the restart as Dylan Collier regathered Knewstubb's drop-kick to sprint in for the Kiwis' fourth try.
Curry muscled his way from short distance for his second try to rub salt into the wounds of an outplayed Britain team.
