Holders Fluminense were upset 2-0 at home by Santos while Corinthians beat Gremio 2-1 away thanks to a fine performance from striker Liedson.
Ronaldinho, who had disappointed Flamengo fans with his indifferent form since joining from AC Milan in January, scored a brilliant goal and laid on another for Diego Mauricio with a one-two inside the box.
"That's as good as it gets. To return scoring a goal, laying on another after a long time is marvellous," Ronaldinho told reporters.
"I'm going to try to go after the conquest that's missing from my curriculum," added Ronaldinho, who had been criticised and jeered by fans after Flamengo's Copa Brasil elimination earlier in May.
Dagoberto opened the scoring in the 34th minute, finishing a good move involving Casemiro and Lucas, who increased Sao Paulo's lead four minutes after the break with a solo run and shot into the roof of the net.
"We want to get rid of that poor phase we've had in the first half of the year and from here on it's only victories. Sao Paulo are a big team, with tradition and only we players can charge our situation," Lucas told reporters.
Santos, resting several leading players for Wednesday's Libertadores Cup semi-final first leg against Paraguay's Cerro Porteno, drew 1-1 at home to Internacional, while Cruzeiro went down 1-0 away to promoted Figueirense.
