Italian Prime Minister Matteo Renzi won by a landslide in weekend EU elections, bolstering his reforms and turning his Democratic Party into the leading light of Europe's left.

Acing a key electoral test for the new government, the party scored 40.8 percent in Sunday's vote, crushing Beppe Grillo's eurosceptic Five Star Movement at 21.2 percent.

Disgraced former prime minister Silvio Berlusconi, who was banned from voting or running because of his tax fraud conviction, came in a distant third with 16.8 percent.

"A historic result. Moved and determined now to work for an Italy that will change Europe," the 39-year-old Renzi -- Italy's youngest-ever prime minister -- tweeted on Monday.

"Italy is stronger than the fears that traverse it and it decided to make a difference in Europe," he said at a press conference in Rome, adding: "Italy now has the task of showing that is a leader, not a follower in Europe".

As he left his home in Genoa, ex-comedian Grillo smiled but made a stab to the heart gesture and later cited Rudyard Kipling's poem "If" about conquering adversity on his blog.

Analysts said Italy's PD was now "the number one progressive party in Europe" following major setbacks for fellow leftists in other European countries.

The score would give the Democratic Party 31 European lawmakers -- the highest number in the Socialist camp -- ahead of the German SPD with 27 European lawmakers.

Turnout was 58.7 percent -- one of the highest in Europe.

Investors broadly welcomed the result, with the Milan stock market opening 2.2 percent higher after a rocky performance in the run-up to the vote because of instability fears.

It was the first time Italians had gone to the polls since the 39-year-old Renzi replaced his predecessor Enrico Letta through an ouster within the Democratic Party earlier this year.

"There is no doubt that this result gives Renzi legitimacy," La Repubblica editor Ezio Mauro said.

Opinion polls had indicated the result would be a close run between Renzi and Grillo and the outcome was all the more surprising as governing parties were punished across Europe with the exception of German Chancellor Angela Merkel's CDU.

- 'Appeal to hope and optimism' -

Renzi had portrayed the contest with Grillo, who won 25.5 percent in a 2013 general election with a campaign against political perks, as "a match between hope and anger".

Grillo had called for a referendum on euro membership and for the scrapping of EU debt reduction targets and his newly-minted lawmakers -- referred to as "grillini" -- will be joining the European Parliament for the first time.

Analysts said the result showed Grillo's M5S party had lost support but had cemented its status as the second biggest party, ahead of Berlusconi's centre-right Forza Italia.

"It's something that reflects a general malaise. It will become a fundamental political player in our country," said Piero Ignazi, a politics professor at Bologna University.

The anti-euro Northern League party, which has promised to ally itself with France's surging National Front, came fourth in the vote with a higher than expected 6.2 percent.

It was followed with 4.4 percent by the New Centre-Right, a junior coalition partner in Renzi's government, and with 4.0 percent by the far-left "Other Europe" party.

Around 30 percent of the vote went to eurosceptic parties.

Stefano Folli from Il Sole 24 Ore business daily said Renzi had been presented with "a truly historic opportunity".

"For the first time, a leader of the centre-left has the power and the means to reform the country," he said.

Several analysts including Folli compared the score to Berlusconi's start in politics in the early 1990s when he beat the left with promises to modernise Italy.

The irony could not be more stark 20 years later as Berlusconi does community service in a hospice after being ejected from parliament over his criminal conviction.

Berlusconi is now "more dead than alive", read a headline in the Il Fatto Quotidiano daily. Folli said the 77-year-old tycoon's "personal star has been extinguished".