The 19-year-old Sao Paulo forward Lucas capped off an exhilarating run from Brazil's own half with a well-placed shot nine minutes after the break.
Neymar added the second for the hosts in the 76th minute from close-range after a low cross from the left from substitute Diego Souza to thrill home fans in the Amazonian city.
While Argentina had virtually no senior players on the field, Brazil were boosted by former FIFA player of the year Ronaldinho and 19-year-old Neymar, who has become a first-choice player in the national team despite his youth.
Brazil missed out on an early goal when Neymar just failed to connect with a cross in front of the goal-line. Captain Ronaldinho also had a chance go begging from a free-kick that sailed just over the bar.
Ronaldinho, who has been in fine form for Brazilian championship contenders Flamengo, was recalled to the national side earlier this month for the 1-0 friendly win over Ghana in London, his first start in nearly a year.
The former Barcelona forward, a World Cup winner in 2002, is now seen by Brazil coach Mano Menezes as a mentor for the new generation of players being groomed in the lead-up to the 2014 World Cup on home soil.
"It's wonderful to play with Neymar and Lucas, the young talents... I was called here for that, to give support to these young people," Ronaldinho told reporters, adding that he was targeting a spot on the team for the London Olympics next year as one of the three permitted over-23 players.
"I go step by step, my dream now is to win the Olympic gold that is missing in my career, and then get really well in the 2014 World Cup," he added.
The match in Belem was the second leg of a friendly tournament held annually with only home-based players. The teams drew 0-0 in the first on September 14 in Cordoba, Argentina.
