Some 30 motor-homes line the famed Atlantica Avenue with Argentine license plates showing they drove a long way to see their heroes Lionel Messi, Sergio Aguero and Angel di Maria.
The rivalry between the two South American nations reaches fever pitch when it comes to football.
Argentines say Diego Maradona is the greatest of all time, Brazilians have Pele. This time, it's Messi versus Neymar.
The contest could very well be settled with a potential clash of the titans at the July 13 final at the Maracana on July 13, a dream scenario for many fans.
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"It took us three days to travel and we spent last night in tents (Saturday) on the beach," he said near the Copacabana Palace hotel where one night costs $1,350 (1,000 euros) during the World Cup.
Roman and fellow Argentines prepared an Argentine "asado" barbecue between two cars with the renowned beef of their homeland.
Even beef, it seems, is a matter of competition.
"The meat here is no good. They don't cut it well," he said as the group drank a cola-based Argentine cocktail, though he hailed the "wonderful welcome" Brazilians have given them.