Fiji had won all 17 of their previous matches in the Olympics and were hot favourites to complete a hat-trick of titles against a team that did not even qualify for Tokyo, but the bookmakers reckoned without the remarkable Dupont.
He might have been on the pitch for only seven minutes but Dupont’s impact was immense, tearing open a game level at 7-7 by setting up the try that put France ahead and then scoring two himself.
It sparked an extraordinary scenes, as the crowd roared and the players danced on the pitch.
"When I came the first day I wondered what I was doing here, if I made the choice to not play the Six Nations was the good one," Dupont said.
"We knew that physically we would be better at the end of the match. We had solid and efficient principles. Team spirit was remarkable.
"I've rarely heard such an atmosphere here in Stade de France. They made a lot of noise and we had to give them back, to put this Olympics on the right rails."
The night had begun ominously for the hosts and the desperately expectant 67,000-crowd as, after starting slowly in their previous games, Fiji hit the ground running when Joseva Talacolo finished off a classic move two minutes in.
France kept their composure though and the home fans exploded when Jefferson-Lee Joseph dived between the posts and Rayan Rebbadj converted to level the scores at halftime.
Both countries’ prime ministers were in the stadium but there was no question about who was the most popular man in France when Dupont joined the fray for the second half.
The man who missed the Six Nations to throw his weight behind the sevens campaign, had an immediate impact as he scampered down the left wing and cleverly fed Aaron Grandidier Nkanang for France’s second try, which Paulin Riva converted.
He then barrelled over himself to break Fiji's resistance and the delirious fans almost took the roof off when Dupont took a tap penalty to crash over again in the final play of the match.
“It was not what we wanted but France were too good for us today," said Fiji's Jerry Tuwai, after adding a silver to his two golds. "We started really well but a lot of things happened that didn’t go our way. I wanted to end my career with another gold but not everything goes to plan."
Earlier, South Africa beat six-man Australia 26-19 with a last-play try by Shaun Williams to take the bronze medal.
The three-day women's competition gets underway on Sunday.