Great Britain guaranteed a gold or silver medal in the men's rugby sevens competition after beating South Africa 7-5 at Deodoro Stadium.
Dan Norton's second-half try, converted by skipper Tom Mitchell, took Britain into the final, where they will play Fiji later on Thursday.
South Africa captain Kyle Brown gave South Africa an early lead in a tense semi-final clash, but Britain responded strongly after trailing at the interval.
And Norton's score, which once again illustrated his blistering pace, was enough to steer Britain onwards to a showpiece encounter on rugby's return to the Olympics for the first time since 1924.
Fiji guaranteed the country a first Olympic medal in any sport by seeing off tournament surprise package Japan 20-5, and they will start the final as favourites.
Japan, meanwhile, will face South Africa in the bronze medal match.
Bibby admitted that he thought Britain's run in the competition might have been coming to an end before he struck with the decisive score to sink Argentina.
"I thought that our Olympic dream was over, but luck was on our side," he said.
"When the full-time whistle went, everyone stayed calm. We just kept working hard, and I was just in the right place at the right time.
"As I went over the line, I was just thinking 'don't drop it.'
"I have never played in a game like that. I have played (sevens) three or four years, and I have never been in a 0-0 draw at full-time.
"Fair play to Argentina. They stuck in it and worked us. We kept our composure and got the crucial score.
"We have only been together for 10 weeks, and to fight out there on the field, no matter what nation you are from - England, Scotland or Wales - is what a true team is about."
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