"Berlusconi is the number one adversary. Monti's objective is in part a clear attempt to destroy him politically," Stefano Folli, political commentator for Il Sole 24 Ore newspaper, told AFP.
The outgoing premier, who resigned on Friday after 13 months at the head of an unelected team of technocrats to take the helm of a caretaker government, said on Sunday that he would consider leading a pro-reform coalition in elections set for 24 to 25 February - though not as a formal candidate.
He cannot officially run in the polls as he is already a senator for life, but under Italy's electoral system he can join the campaign, add his name to ballot lists and be asked to lead the country by whoever wins.
"Monti has thrown his hat into the ring because he wants to stop Berlusconi and he does not think the centre-left could get enough votes for a majority," said Roberto D'Alimonte, politics professor at the Luiss University in Rome.
While opinion polls had previously tipped former communist Democratic Party leader Pier Luigi Bersani to win, Monti's announcement could turn the election into a nail-biting three-way race.
Monti, 69, said on Sunday that he would be ready to lead those who agree with his proposals to "change Italy and reform Europe".
"He wants to be a guiding star, leading everyone up the only path for Italy" where the threat of the Eurozone debt crisis remains, said Valentino Parlato, the founder of the radical left-wing Manifesto daily.
Monti's speech on Sunday directly took on Berlusconi, who has launched his sixth election campaign in two decades and hopes to become prime minister for a fourth time.
Berlusconi on trial
The conservative media tycoon, who is appealing an October conviction for tax fraud and is currently on trial for having sex with an underage prostitute, had made proposals including the abolition of a new property tax that Monti called "very dangerous and illusory".
A Monti-backed reform coalition is likely to steal votes from both Bersani and Berlusconi, who has virulently lambasted Monti's pro-Europe austerity policies.
Franco Pavoncello, professor of politics at the John Cabot American University in Rome, called Monti's descent into the political fray "inevitable".
"It was an act of conscience, driven by serious concerns that the reforms carried out this year are at risk under a new government, and a desire to avoid the age-old campaign between Silvio Berlusconi and the centre-left," he said.
Monti's announcement was met with confusion, with Italian media lamenting his ambiguity and dubbing him a "reluctant candidate" whose unorthodox bid made no apparent effort to reach out to potential voters.
"At the end of the day, Mario Monti will be a non-candidate candidate," wrote the leading daily Corriere della Sera, adding that the former high-flying European commissioner was entering politics "in a fog where potential voters risk getting lost."
Folli said Monti had "put himself forward as a new political character, but cannot stop here. He needs to explain himself more clearly to Italians."
Election race
According to D'Alimonte, "Monti is calling on Italian moderates to follow him, with the aim of then forming a coalition with the centre-left," while Folli said that even 15 to 20% of the vote would be enough to form a pro-European alliance with the left.
Pavoncello said the issue is not whether Monti will win the race.
"No one expects Monti to win the election, but he could have a serious impact on shaping the political geography of the country, especially by cutting Berlusconi down to size," he said.
Should Monti not win, he could still be appointed to finance minister if the centre-left wins in February.
Monti, who has been endorsed by European leaders, the markets and the Roman Catholic Church, "could still be the architect of a pro-European political economy for Italy," Folli said.