Corinthians, who won nine of their opening 10 matches, were unconvincing in Wednesday's 2-1 home victory over bottom team America-MG.
Flamengo, with Ronaldinho inspirational once again, beat Cruzeiro 1-0 away at the Alligator's Arena in Sete Lagoas for a third consecutive win that kept them one point behind the leaders.
Corinthians' Jorge Henrique scored the fastest goal of the championship to put them 1-0 up after 28 seconds at the Pacaembu in Sao Paulo when he got a touch to William's diagonal shot.
However, the team played poorly and allowed the visitors to equalise with a header from striker Kempes in the 15th minute.
Midfielder Paulinho scored the winner in the 67th from a free-kick by Alex and America had Gilson sent off for a second booking but still Corinthians failed to dominate.
Unbeaten Flamengo scored in first-half stoppage-time when striker Deivid netted with a right-foot shot from a fine pass by Ronaldinho, the championship's top scorer with nine goals whose form could earn him a recall to the Brazil team.
South American champions Santos lost 2-0 at third-placed Vasco da Gama, their sixth defeat in 11 matches and third in a row, and are in the relegation zone.
