Italy's new Premier Romano Prodi on Friday won a crucial confidence vote in the Senate, where his centre-left coalition holds just two more seats than the opposition.
Prodi's government was approved by a vote of 165 to 155 with no abstentions after the chamber's seven life senators all voted in favour of the government.
His government has to clear the Lower House in another confidence vote scheduled for Tuesday.
The life senators, including the Nobel laureate Rita Levi Montalcini, the seven-time premier Giulio Andreotti and the former president Carlo Azeglio Ciampi, were jeered and whistled by the opposition as they voted.
After the Senate Speaker Franco Marini failed to call the opposition to order, a scuffle broke out between two senators.
The confidence vote is usually a straightforward affair but Prodi's fragile hold over the 322-seat Senate transformed the ballot into a tense test which could have toppled the government just two days after it was sworn into office.
Prodi won the narrowest of victories against the former premier Silvio Berlusconi in Italy's April general election following a campaign seen as the most acrimonious in postwar Italy.
Berlusconi refused to concede defeat, even after the Supreme Court confirmed Prodi's win following a review of disputed ballots.
The billionaire media magnate has vowed to exploit Prodi's weak parliamentary majority and battle the government at every possible turn.
Under a controversial electoral reform law, forced through by the centre-right just before the election and returning Italy to proportional representation, Prodi has a relatively solid hold over the Lower House even though he won there by just 25,000 votes.
But in the Senate, where he lost the popular vote, Prodi has 158 seats to Berlusconi's 156.
However, most of the seven life senators are expected to continue supporting the government together with another independent senator voted in by Italian residents abroad.
Italian political analysts said Prodi's weak majority and his disparate nine-party coalition - which ranges from Communists and anti-clericalists to staunch Catholics - could prevent him from governing effectively and passing any far-reaching reforms.