Fluminense remain six points ahead of second-placed Mineiro after Brazil striker Fred settled his second Rio derby in a row with the only goal in a 1-0 win over Botafogo.
Former FIFA player of the year Ronaldinho opened the scoring for Mineiro, who had not won in their previous four matches, with a shot from outside the box into the top corner that looked at first like a cross.
Ronaldinho, who joined Mineiro from Flamengo this year, added a free-kick and completed his treble with a penalty. He also laid on goals for defender Rever and striker Bernard before Carlos Cesar completed the rout.
Fred, whose goal won the derby against Flamengo last weekend, scored in the 72nd minute at the Engenhao in Rio, beginning a counter-attack in midfield, taking a return pass from winger Wellington Nem and slotting home.
Both goalkeepers made brilliant saves with Flu's Diego Cavalieri stopping shots from midfielders Fellype Gabriel and Elkeson after they had been set up by Dutchman Clarence Seedorf.
Botafogo's Brazil keeper Jefferson made a spectacular save to keep out a header by defender Digao from playmaker Deco's cross three minutes before being beaten by Fred.
Brazil striker Luis Fabiano scored twice for Sao Paulo who beat 10-man Palmeiras 3-0 in their derby to increase their city rivals' relegation worries. In between, ex-Arsenal midfielder Denilson hit Sao Paulo's second from outside the box.
Palmeiras had defender Jose Manuel Barbosa sent off in the 53rd minute for a second booking.