Prime Minister Silvio Berlusconi was "surprised and saddened" after his centre-right bloc lost ground in local elections and was forced to trail in a run-off in his powerbase, financial capital Milan.
Milan's centre-right mayor Letizia Moratti won 41.6 percent of the vote in elections on May 15-16 against 48 percent for her rival Giuliano Pisapia, giving the left a chance to win for the first time in nearly 20 years in a run-off in two weeks.
But Berlusconi was the main loser, failing to convince voters to deal him an outright victory in his home town Milan.
"Milan turns its back on Berlusconi", "Berlus-crack" and "Shock for Berlusconi in Milan" were among front page headlines in Italian papers on Tuesday.
"The run-off in Milan doesn't humiliate the outgoing mayor as much as it humiliates Silvio Berlusconi ... who gets a slap in the face on a personal and political level," wrote Massimo Franco in Italian daily Corriere Della Sera.
The surprise results point to a second round on May 29-30, giving the centre-left its best chance since 1993 of winning the city where Berlusconi built his business empire and later launched his political career.
They also confirmed the indications from opinion polls showing Berlusconi's popularity has been undermined by a sex scandal, three corruption and tax fraud trials and a faltering economy.
"He is saddened, surprised and saddened. He did not expect a result like this," the premier's aides told Italian news agency ANSA. Berlusconi's spokesman said the prime minister would comment on the ballot on Tuesday.
His main ally, the pro-devolution Northern League, fared worse than expected in its own heartland - a factor likely to complicate already strained relations with Berlusconi.
The centre-left swept up Turin and won a first-round victory in its stronghold of Bologna, while Berlusconi's PDL party led in Naples, which is also set for a run-off in two weeks.
The four cities were the most important contests in the elections in 1,310 towns and 11 provinces, a test for Berlusconi midway through his term.
"The wind in the north is blowing against the PDL and the League," said Pierluigi Bersani, leader of the largest opposition party, the PD.
Four concurrent trials, including one on charges that Berlusconi paid for sex with an underage prostitute, have pushed his approval rating to about 30 percent, the lowest since he swept to power for the third time in 2008.
The premier, who denies all charges and says politically biased magistrates are hounding him, appeared in court on Monday in a hearing into bribery charges.
Berlusconi is also taking the heat for failing to revive Italy's chronically low growth. The economy expanded just 0.1 percent in the first three months of the year, well below rates in Germany, France and even crisis-hit Greece.
The League, which is vital for Berlusconi's survival after a split in the ruling PDL party last year, has marked its distance from the premier on several issues in recent weeks, notably opposing Italy's involvement in the NATO bombing of Libya.
The League had hoped to cash in on Berlusconi's weakness, but it failed to boost its share of the vote in the big cities. In Milan and Turin it won less than 10 percent support.
Not everything was good news for the divided centre-left opposition, however.
In Milan, the PD only belatedly rallied behind frontrunner Pisapia, who was not its designated candidate. In Naples, where a long-running garbage crisis has embarrassed the centre-left local authorities, its man was overshadowed by a leftist outsider and will be excluded from the run-off.