Mr Grillo's Five Star Movement had 25.54% and the centrist list led by Mario Monti 10.57%.
But his approaches to Mr Grillo appear so far to have fallen on deaf ears.
Mr Grillo said the M5S would decide whether to support specific legislation on a case-by-case basis.
Most striking is the Cinque Stelle, or 5-Star, movement, organised by satirist and comedian Beppe Grillo.
It is possible that the wild-haired Mr Grillo might get more than 20% of the vote.
All the candidates, with the exception of Grillo, cast their ballots Sunday, ANSA reported.
"Italy has taken a step forward, " said Davide Barillari, a candidate for Mr. Grillo's Five-Star movement.
Opinion polls suggested there would be a strong turnout for comedian Beppe Grillo's anti-establishment movement.
BBC: Italy votes in election seen as key for economic recovery
Mr Grillo wants to tear down the political establishment but is largely silent about what might follow.
The wild-card party of Beppe Grillo, the grass-roots Five-Star Movement, will also not enter into an alliance.
There is one leader who does not wear a Marinella tie - Beppe Grillo doesn't do ties.
The wild card in this campaign is Beppe Grillo, a comedian who rages against the political establishment.
Led by its guiding star, the comedian-turned politician Beppe Grillo, it was born and bred on the internet.
What will become clear in the next week is how far Grillo is prepared to take his movement.
During one performance Grillo smashed a pile of computers on stage while lamenting modern society's dependency on technology.
And as Grillo has written, many people didn't trust the police and the soldiers as they once did.
Stefano Rodota, the candidate backed by former comic Beppe Grillo's 5-Star Movement, came in second place with 240 votes.
As well as talks with Mr Bersani on Thursday, Mr Napolitano will consult with Mr Berlusconi and Beppe Grillo.
Many demonstrators were supporters of Beppe Grillo, the leader of the 5-Star Movement.
The projected results showed more than half of Italians had voted for the anti-euro platforms of Berlusconi and Grillo.
FORBES: Italian Elections: The Real Problem Is The Primary Surplus Means Italy Can Leave The Euro
The seats under Mr Grillo's control in both houses could therefore prove crucial in making any coalition government viable.
One unanswered question is whether Beppe Grillo will be open to a deal.
Mr Grillo later insisted that his words had been taken out of context.
BBC: Italy President Napolitano calls for realism after vote
Small wonder voters have been turning in frustration to the outsider Mr. Grillo.
While there is little doubt Grillo can entertain a crowd, questions remain over whether he can destabilize mainstream Italian politics.
CNN: Beppe Grillo: Clown prince takes Italian election by storm
Grillo has railed against big business and the corruption of Italy's political establishment, and holds broadly euro-skeptical and pro-environmental positions.
M5S grew out of the equally remarkable success of an anti-establishment blog written by Beppe Grillo, a comedian (pictured above).
The leader of the centre-left, Pier Luigi Bersani, said that Mr Grillo risked taking Italy down the same road as Greece.
Lawmakers from Parliament's third-largest bloc, the anti-establishment 5 Star Movement led by comic-turned-political agitator Beppe Grillo, galvanized supporters for the protest.
Five Star, led by former comedian Beppe Grillo, won an unexpected 25% in the election and holds the balance of power.
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