Many fans came to the Maracana Stadium to watch Lionel Messi in his likely last match in Brazil, a superclasico in World Cup qualifying against the hosts.
Instead, they saw Nicolas Otamendi score the only goal in a 1-0 win for Argentina after a brawl between fans that delayed the start of the game.
The World Cup champions inflicted the first home defeat on Brazil ever in World Cup qualifying. It was Brazil's third consecutive loss in the round-robin tournament - another negative mark for new coach Fernando Diniz.
Messi left the pitch in the 78th minute amid a mixture of jeers and applause from Brazil fans. Dozens of children arrived at the Maracana wearing the shirts of Barcelona, the star's previous club, and Inter Miami.
The Argentine star wasn't able to end one of his last barriers in the sport at the Maracana, though, to score against the Brazilians in a World Cup qualifier.
Argentina will return home not only atop the South American qualifying standings but also having given their fans one more chance to celebrate a victory at the historic stadium in Rio de Janeiro. Two years ago, Angel di Maria scored the only goal in an empty Maracana to give his team the Copa America title.
The violent pre-match incident, starting shortly after the national anthems, stalled the start for 27 minutes. Argentina, led by Messi, headed to the locker rooms for 22 minutes. At least one fan left the stadium bleeding from his head. Rio police said they had arrested eight people due to the brawl.
The aggression between fans was reflected on the field in the first 20 minutes of the encounter; the referee gave fouls against Brazil during that time. The tension eased and allowed Argentina to avoid direct confrontation.
Brazil wasted opportunities, with Raphinha's free kick in the 38th minute and Cristian Romero saving Argentina near the goalline six minutes later after a crossed shot by Gabriel Martinelli.
Brazil suggested they would keep the pressure after the break. Rodrygo forced goalkeeper Dibu Martinez to a close-range save in the 54th.
But Argentina's goal in the 63rd with a header by Otamendi, who jumped above the Brazilian defenders to meet a corner kick, was one of the few chances the team created.
Teenager Endrick, one of Brazil's big hopes up front, didn't make much difference after he went on in the 72nd.
In the 81st, midfielder Joelinton, who had just stepped in as a substitute for Brazil, was sent off after pushing Rodrigo de Paul. Brazil fans ended the match chanting ole for every touch of the Argentinians, while the visiting supporters waved their shirts as some of their players celebrated on the pitch.
Argentina lead the 10-team South American qualifying competition with 15 points from six matches, followed by Uruguay on 13 and Colombia. Brazil could end the year in sixth position, with seven points.
The 2026 World Cup in the United States, Mexico and Canada will include 48 teams, meaning direct entry for the top six teams from South America. The seventh-place team can earn a berth in an intercontinental playoff.
Also on Tuesday, Colombia won 1-0 at Paraguay; Uruguay beat Bolivia 3-0 in Montevideo; and Ecuador topped Chile 1-0.
Peru and Venezuela were still playing at the time the Brazil vs. Argentina match ended.
The seventh and eighth rounds of South American qualifying will take place in September after the next edition of Copa America in the United States.