A quiet game by Ronaldinho, who had inspired Mineiro in the early rounds of the championship, saw the team from Belo Horizonte produce no answers to a headed goal by Paulo Andre from a corner in the 63rd minute.
In an even first half at the Pacaembu in Sao Paulo, Ronaldinho played well and created several chances for the visiting side.
However, he faded in the second half and Mineiro could not even take advantage of an extra man from the 77th minute when Corinthians striker Emerson was sent off after a second booking for handball.
The visitors then had fullback Junior Cesar dismissed for dissent in the 90th.
Mineiro, who had drawn their last two matches, had not lost since the fifth round of matches almost three months ago. They are now equal on 44 points with Fluminense although they have a match in hand.
Fluminense could have gone top but were held 1-1 at home by Figueirense on Saturday.
Uruguay's Diego Forlan scored his first goals for Internacional since joining them from Inter Milan in July, helping the side from the southern city of Porto Alegre crush Flamengo 4-1.
Forlan, the 2010 World Cup's Golden Ball winner as the tournament's best player, equalised on the half-hour after a blunder by Inter goalkeeper Muriel had gifted Vagner Love the opening goal for Flamengo.
Forlan added a second and his team's third in the 66th minute as sixth-placed Inter, 10 points off the pace, romped to victory with extra goals from Josimar and Brazil striker Leandro Damiao.