Italian Prime Minister Romano Prodi's embattled centre-left government won a vote of confidence in the Chamber of Deputies by 326 to 275.
The win in the lower house was expected, as the government coalition has a comfortable majority.
A second confidence motion is set for tomorrow in the Senate, but media reports said Prodi may opt out of that test, lacking the necessary votes, and instead resign.
The defection of a key Senate ally has left the 20-month-old government with a two-seat deficit.
Mr Prodi defended his government's performance in a defiant speech to parliament yesterday.
The crisis for the Prodi government, which ranges from far-left communists to centrist Catholics, was sparked by centrist Clemente Mastella's resignation as justice minister last week.
On Monday his small UDEUR party said it would oppose Mr Prodi in a vote of confidence. UDEUR's three votes have been crucial in the Senate, where the government's survival will now depend on the support of left-leaning senators-for-life.
The Prodi government fell briefly in February last year, but was reinstated after a vote of confidence in the Senate.
If it falls again, President Giorgio Napolitano could call early elections, name a caretaker government or ask the speaker of the Senate or the Chamber of Deputies to form a government.
Mr Mastella resigned after being named in a corruption probe along with his wife. Both have protested their innocence.
Observers say his decision stemmed more from the prospect of electoral reform through a popular referendum later this year that could be the end of small political parties such as UDEUR, which won just 1.4% of the vote in 2006 elections.
