The show of resolve was the latest sign a mounting political crisis over the investigation into alleged embezzlement and bribery at the state oil giant Petrobras was spilling onto the streets.
"We are here out of solidarity," said one man in the crowd, Jesualdo Freitas, 57. He described anger at Lula's brief detention yesterday as having galvanized the left.
"It strengthens the Workers' Party and the movement to defend president Lula," he told AFP.
Until now, the massive anti-corruption scandal has unfolded mostly in the civilized surroundings of courtrooms and lawyers' offices.
But during yesterday's drama, opponents and supporters of Lula and Rousseff scuffled in Sao Paulo. Late in the day, opponents organized on social media to lean out of windows in Sao Paulo, Rio de Janeiro and the capital Brasilia, shouting and banging pots in celebration.
The opposition blames Lula for the gargantuan corruption network uncovered at Petrobras, which was systematically plundered during much of his presidency, with bribes funneling into the pockets of high-ranking politicians, including from the Workers' Party.
The sight of armed police at Lula's home has given opponents a boost as they seek to reignite a stalled impeachment drive against Rousseff and prepare for nationwide demonstrations on March 13.
"The opposition will move with greater strength, with new impetus to try and force out Rousseff," Sao Paulo-based political analyst Andre Cesar said.
Lula, still a powerful speaker at 70, is also spoiling for a fight.
