"Dialogue with Berlusconi? It is very difficult to imagine that Berlusconi would propose useful ideas (for the movement)," said 5 Star Movement candidate Alessandro Di Battista at Rome headquarters. "It never happened until now, but miracles happen."
Italy's borrowing costs have reflected the optimism that the country will stick to its reform plans.
The interest rate on Italy's 10-year bonds, an indicator of investor confidence in a country's ability to manage its debt, fell to 4.19 percent in afternoon trading Monday. Last summer, at the height of concern over Italy's economy, that interest rate was hovering at about 6.36 percent.
Milan's stock exchange closed slightly higher, with the benchmark FTSE MIB up 0.73 percent to 16,351 points.
With 99.7 percent of the lower house vote counted, the Bersani camp had had 29.55 percent of the vote, to Berlusconi's 29.17 percent. Grillo had 25.54 and Monti's alliance 10.56.
In the Senate, near complete Interior Ministry figures showed Bersani and his allies had nearly 32 percent while Berlusconi and his coalition partners were pulling nearly 31 percent. Grillo had more than 23 percent. The overseas Senate ballot was to be added to the total later Tuesday.
More important than the overall national numbers, however, was the state-of-play in large swing regions — and Berlusconi was projected to win those.
Italy's complex electoral law calls for the Senate seats to be divvied up according to how candidates fare region by region, and Berlusconi appeared to be winning big in Lombardy, and also ahead in the closely watched regions of Sicily and Campania, around Naples.
A Berlusconi triumph in those key regions would likely hand him control of the upper chamber, which in Italy's legislative system is as powerful as the lower house.
When Berlusconi was forced out of office in November 2011, he was widely assumed to have joined the political dead. At 76, blamed for mismanaging the economy and disgraced by criminal allegations of sex with an underage prostitute, a comeback seemed impossible.
But one thing has become axiomatic about Berlusconi in his 20 years at the center of Italian politics: Never count him out.
This time around, in an age of wrenching austerity, he had a very simple campaign strategy: throw around the cash.
Berlusconi has promised to give back an unpopular property tax imposed by Monti — with money from his own deep pockets, if need be.
Even his purchase of star striker Mario Balotelli for his AC Milan soccer team was widely seen as a ploy to buy votes. Berlusconi has also appealed to Italy's right-wing by praising Italy's former fascist dictator Benito Mussolini during a ceremony commemorating Holocaust victims.
"He played a very able game," said Walston. "Considering that he didn't fulfill his previous promises, it's extraordinary."
With near complete results, Bersani had a tiny edge in the lower chamber, where electoral law enables the biggest vote-getter there to end up with a bonus of more than 50 percent of the seats.
Monti's centrist coalition was having a terrible election, with his alliance getting roughly 10 percent. Although respected abroad for his measures that helped stave off Italy's debt crisis, the economist has widely been blamed for financial suffering caused by austerity cuts.
Analysts saw two big stories in Italy's election.
"The first is the big surprising increase scored by the 5 Star Movement, and the other is the disappointing result" of Monti's coalition, said Massimo Franco, a columnist with Corriere della Sera.
Berlusconi, who was forced from office in November 2011 by the debt crisis, has sought to close the gap by promising to reimburse an unpopular tax — a tactic that brought him within a hair's breadth of winning the 2006 election. The billionaire media mogul only a few days ago told voters if need be, he'd reimburse the tax to them by shelling out from his own pocket to the tune of several billion euros (dollars).