While several voice regret at the potential damage to the widely popular Lula's reputation, they also argue it also sends a strong signal about the rule of the law in Brazil.
"It is a profoundly sad day, but it also demonstrates the fact that no-one, not even Lula, is above the law," Eliane Cantanhede writes in the Estadao daily.
She adds that there is now a strong possibility that the scandal could give a new impetus to attempts to impeach Ms Rousseff.
Cantanhede also voices the fear that this may be a struggle that plays out through violence on the streets.
"Dilma is totally isolated in her palaces, while Lula is moving away from his 'peace and love' image and calling his troops to war," she warns.
In newspaper Globo, Miriam Leitao says the search of Lula's residence and his temporary arrest - codenamed Operation Aletheia ("Truth" in ancient Greek) - has "raised the political temperature to its highest level".
But she also voices satisfaction that "no-one in the country is an untouchable person anymore, and that is what Aletheia is proving".
Writing in Folha de Sao Paulo, Igor Gielow argues that the latest events will give a powerful boost to the campaign to remove the Workers' Party from power, already fuelled by anger at corruption and the poor economy.
He also predicts that supporters of Lula may still have the strength and support to survive the wider investigation against him - dubbed Operation Lava Jato, or Car Wash.
"Lula is a master of resurrections and has the best-known political resilience in the country - but this could be drowned by the [car wash] water jets," he says.
Speaking on Brazil's Radio CBN on Friday, analyst Merval Pereira said he believed Lula would have a tough fight on his hands.
"The evidence that the prosecutors have gathered is very strong and the former president will probably be tried," Mr Pereira argued.
Journalist Carlos Alberto Sardenberg - speaking to the same station - agreed, saying that investigating authorities must be sure of their data as it "will provoke a strong reaction from the PT, its allies and the government, especially President Dilma Rousseff".
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Brazilian media commentators believe former President Luiz Inacio Lula da Silva's questioning in a major fraud inquiry could have serious repercussions for his future and that of his ally and successor, President Dilma Rousseff.