Palmeiras coach Luiz Felipe Scolari, whose side beat Atletico Paranaense 2-0 on Saturday to end a run of six matches without victory, could be suspended for up to six games after being escorted off for excessive criticism of the referee.
Fluminense took advantage of Inter's decision to field only two first-choice players, goalkeeper Renan and midfielder Tinga, ahead of Wednesday's second leg of the Libertadores Cup final at home to Guadalajara of Mexico.
Inspired by their diminutive Argentine playmaker Dario Conca, Fluminense were dominant from the start and went two up in the opening 23 minutes.
Right-back Mariano's left-footed shot in the 20th minute was deflected past Renan and three minutes later Conca's near-post corner was headed home by striker Washington for the second.
The third goal came on the hour when striker Emerson ran onto a clinical ball from Conca to steer it home.
Inter lost Tinga to injury after 35 minutes and had striker Rafael Sobis sent off two minutes from time for a violent foul on defender Leandro Euzebio.
Flu, whose solitary Brazilian championship title dates back to 1984, have 32 points to 28 for Corinthians, who lost 3-2 at third-placed Avai.
Avai are on 22 and Botafogo, who beat lowly Atletico Goianiense 2-0 on Saturday, completing the top four a point further back.
DECO RECEPTION
Before kick-off, Flu's newly-signed midfielder Deco was greeted with rapturous applause by a crowd of nearly 60,000 at the Maracana.
The former Porto, Barcelona and Chelsea player will make his debut next weekend's in the derby with Vasco da Gama at Rio's giant stadium.
"This is all fantastic. I've never experienced anything like it before and I hope to repay this affection with titles," the 32-year-old, back in the country of his birth after 13 years in Europe, told reporters.
The demonstrative Scolari, who was Deco's coach with Portugal and Chelsea, has found it hard to contain his his feelings due to his team's lowly position and the fear of relegation.
He was sent to the stands in the 69th minute after repeatedly complaining to the referee but he stopped behind one of the goals for several more minutes, shouting instructions to his players and had to be removed by the fourth official.
Palmeiras are now just two points behind fourth-placed Botafogo, Cruzeiro and Ceara and five clear of the drop-zone.
Interact: Twitter * Facebook *Forums
