Brazil forward Neymar scored a hat-trick to lead Santos in a 3-1 win over Sao Paulo while former Brazil and Real Madrid coach Vanderlei Luxemburgo was sent off following a row with a ball boy in Gremio's match.
Luxemburgo rushed out of his technical area and ran down the touchline to confront the ball boy by the corner flag, leading to an incident which held up the Porto Alegre derby against Internacional for five minutes and involved around 30 people.
He was apparently angry because the ball boy, employed by Internacional, placed the ball for a corner to be taken by the hosts while Gremio's defence were out of position.
As Luxemburgo approached the ball boy, International players joined in along with police, radio reporters and cameramen, leading to a huge melee.
""I regret the incident, I'm the one to blame," Luxemburgo told reporters. ""It all happened in the heat of the moment."
Internacional players later ran to celebrate with the ball boy after Fabricio grabbed a late goal to give them a 2-1 win in the Gaucho championship, one of the plethora of state competitions which kick off the marathon Brazilian season.
Gremio were also angry to find that salt had been sprinkled under their bench before kickoff, a practice which in Brazilian football folklore is said to bring bad luck to the victims.
Neymar's afternoon got off to a quick start when he converted a penalty in the first minute for Santos, firing into the roof of the net.
The 20-year-old struck again in the 32nd minute when he collected the ball in midfield, outran his marker and slipped the ball past goalkeeper Denis.
Although William Jose pulled one back for Sao Paulo after the break, Neymar completed his hat-trick with a shot from the edge of the area which slipped through the hands of the keeper.
Sao Paulo often found Neymar unplayable and their frustration boiled over when defender Ivan Piris was booked for blatantly hacking him down after the striker dribbled past him four times in succession.
Sao Paulo later had Cicero sent off for another foul on the Santos prodigy.
Guarani, who beat Ponte Preta 3-1, will face Santos in the final of the competition.
Uruguay forward Sebastian Abreu scored twice to give Botafogo a 3-1 win over Vasco da Gama to win the second stage of the Carioca championship in Rio de Janeiro.
Under the tournament format, Botafogo will face Fluminense, who won the first stage held earlier in the year.