Now Berlusconi has performed an astonishing comeback to return to the spotlight, exacting his political revenge while Monti is struggling badly to make a breakthrough in the campaign for a Feb. 24-25 election.
For most of 2012 Monti, a former European commissioner, dominated Italy, pushing politicians to the sidelines and restoring the country's battered reputation after Berlusconi had taken the country to the brink of a Greek-style crisis.
Monti, already a Brussels insider, was feted in European halls of power for his austerity policies after the banishing of Berlusconi. Businessmen clamoured for him to stand for a second term.
But since Monti responded to huge domestic and international pressure in December and dived into Italy's murky politics as leader of a centrist coalition, his trajectory has flattened as Berlusconi and other seasoned politicians strike back.
"Monti is not a politician at all. He was good at trying to govern this complicated country but he is definitely unable to campaign," said Gianfranco Pasquino, a political science professor at Bologna University.
"A professor of economics who has spent all his life in European activities, or teaching, or giving advice to banks cannot become a good campaigner in less than a month."
Monti's popularity has fallen from 70pc when he took over as premier in November 2011 to as low as 30pc now.
His failure to gain traction is down to a combination of factors including the extreme difficulty of occupying the centre in Italy's bipolar system and the short time he had to campaign.
But he has also made errors including a bad choice of allies, that reveal his lack of political experience, while his popularity with foreign leaders is a hindrance rather than boon in the campaign, prompting him this week to sharply tell EU officials to stop intervening on his behalf.
In fact it is arguable that Monti may have had a greater chance of influencing Italy's future if he had not entered the campaign at all and remained above the fray to line himself up as state president or another independent role.
"He has lost his political virginity and cannot be used any more as an impartial saviour," said Professor James Walston of Rome's American University.
Berlusconi's trajectory has been in the opposite direction. After withdrawing to the shadows for much of 2012, by the autumn he looked like an old, weary man, pushing his PDL party towards disintegration by his indecision.
But the billionaire showman has staged an extraordinary bounce-back in the last month, blitzing television programmes in a remarkable display of media savvy and stamina for a man of 76.
"It was a great surprise. I didn't believe he was capable of it at his age ... On the technical level of communication he is very good," said prominent pollster Renato Mannheimer.
Despite being harried by a lurid sex scandal, Berlusconi has added from three to five percentage points to his People of Freedom party's support - some polls say more - although his progress has now slowed and may have peaked.
With the centre-left parties hanging on to a clear lead, there still seems only a small chance that Berlusconi will win the election, experts say, and he is fighting a bitter battle with Monti to control the balance of power.
While it is undoubted that Berlusconi has revived the centre-right, Monti has struggled to meet extravagant expectations that he could sweep away a deeply discredited political system and set Italy on a radical new path of renewal.
Support for his centrist alliance looks stuck around 15pc, well short of his target of 20pc. "He will get even less than 15pc," Maurizio Pessato, vice president of SWG polling company, told Reuters.
Monti is under threat for third place from the anti-establishment 5-Star Movement of Beppe Grillo, the comedian who has exploited deep voter anger over Monti's taxes, economic hardship and a string of political scandals.
The raging scandal over the world's oldest bank, Monte dei Paschi di Siena, has hurt the centre-left Democratic Party with which it has historic links, but also damaged Monti, seen by some voters as a member of an elitist financier class.
As a technocrat saviour, Monti's aloof, professorial manners incurred respect, but they are much less suited to the cut and thrust of politics.
In contrast, Berlusconi is a political master, with enviable communications skills and an ability with a ready quip to exploit his image among many conservative voters as a lovable rogue.
Monti seems to have difficulty finding the right tone, veering between his trademark "English" politeness and aggressively attacking his opponents while never departing from a dry monotonous tone, earning a nickname among some politicians as "Dr Jekyll and Mr Hyde."
He called Berlusconi a Pied Piper tricking Italians. Berlusconi shot back that Monti would try to tax his flute.
"Monti's biggest error is to have changed his style. To start criticising his opponents using words that do not really belong to the lexicon of a competent technocrat, that an austere professor of economics should not say," said Pasquino.
Berlusconi has attracted support with a constant mantra of attacking the "little professor" over a hated housing tax and calling him a puppet of German Chancellor Angela Merkel.
But whereas Monti is seen as justified in giving as good as he gets from Berlusconi, his attacks on the mild mannered centre-left leader Pier Luigi Bersani, especially over Monte dei Paschi, often sound sour and could be counterproductive.
Monti's suggestions that Bersani is dominated by the unions, should "clip the wings" of extremists and dump his leftist ally Nichi Vendola because he would spook markets have pushed even the centre left leader into angry responses.
This could be damaging because Monti's best hope is to win enough power to oblige Bersani to invite him into a coalition government - something which advances by Berlusconi in the Senate could ironically make more likely.
Monti's real mistake may be that he took on a near impossible task, trying to turn Italian politics upside down in barely two months after launching his bid too late, and making a fundamental mistake in how he chose his allies.
Allying with Casini, who has barely got above 5-6 percent of the vote in 20 years in politics, and house speaker Fini who commands even less, may have been a fatal error because it blew Monti's chances of appearing as something radically new.
"Proposing himself as different from the others and from outside politics is denied by the fact that he is allied with two representatives of very old politics," Pessato said.
He said Monti and his political outsider backers, including Ferrari boss Luca Cordero di Montezemolo, "should have had the courage to go for it without getting in the same boat as Fini and Casini. They were too timid, both Monti and Montezemolo."
But even without these mistakes, Monti would have faced a desperately uphill task to change the postwar Italian division between a broad right and broad left.
"He found himself trying to navigate in the centre of a canal without getting too close to either bank ... his position was very, very difficult," Pessato said.