UPDATE 2-Italy's center-right ahead in mayoral vote run-offs

* Vote comes ahead of national election due by May 2018

* Results look likely to be a setback for ruling Democratic Party (Updates with early results)

ROME, June 25 (Reuters) - Italy's center-right parties performed strongly in mayoral elections on Sunday, early results showed, in a vote likely to put pressure on the center-left government ahead of national elections due in less than a year.

In the most closely watched contest, the northern port city of Genoa - a traditional left-wing stronghold - seemed set to pass to the center-right for the first time in more than 50 years.

The candidate backed by the anti-immigrant Northern League and Silvio Berlusconi's Forza Italia party will get around 54 percent of the vote, compared with 46 percent for the candidate backed by the ruling Democratic Party (PD), according to the first projections based on the actual vote count.

The results are shaping up as a setback for PD leader and former Prime Minister Matteo Renzi, who has taken a back seat in campaigning for the mayoral elections after seeing his party roiled by internal divisions this year.

"If these results are confirmed it will show the wind is blowing in favor of the center-right from the north to the center to the south, this would be an extraordinary victory," said Renato Brunetta, the lower house leader of Forza Italia.

Around 4.3 million people were eligible to vote in municipalities still up for grabs because no candidate won more than 50 percent in the June 11 first-round election.

The anti-establishment 5-Star Movement, which is Italy's most popular party nationwide according to some opinion polls, performed very badly in the first round and only made the run-off in one of the 25 largest cities.

The early results on Sunday also put center-right candidates clearly ahead in the northern city of Verona and in Catanzaro in the south.

It also led in the central city of L'Aquila, another recently center-left stronghold where the center-left candidate had led after the first round.

Final results are expected to be known early on Monday.

Italy's national parliamentary election must be held by May 2018 but the broad coalition backing Prime Minister Paolo Gentiloni is fragile and political analysts say an early vote this autumn cannot be ruled out. (Reporting by Gavin Jones; Editing by Jane Merriman and Andrew Hay)