Rome elected populist Virginia Raggi as its first female mayor in a significant electoral reverse for Prime Minister Matteo Renzi.
Exit polls gave the anti-establishment Five Star Movement's candidate at least 60% of the vote in a run-off contest with Roberto Giachetti of Mr Renzi's centre-left Democratic Party (PD).
The lawyer and local councillor, a complete unknown only a few months ago, had been widely expected to claim the keys to City Hall.
But the margin of her victory exceeded expectations with the exit polls pointing to her taking between 62-68% of the vote.
Polls suggested the PD had not suffered such big reverses elsewhere but the centre-left was in danger of losing control of the major northern cities Milan and Turin while holding on to Bologna and Naples.
Victory in Rome is a major coup for the Five Star Movement (MS5) founded by comedian Beppe Grillo in 2009, which has since established itself as the major opposition force in Italian politics.
Ms Raggi successfully tapped into widespread anger among voters over the state of the capital's public transport and other services, widely seen as having been undermined by years of cronyism and sleaze in the municipal administration.
