By Michele Kambas and Renee Maltezou

ATHENS A resounding defeat of radical parties in Greece's election on Sunday has shown voters have mellowed after more than 15 years of fuming over austerity triggered by a crippling debt crisis.

The conservative New Democracy party romped to victory with 40.8% of the vote in Sunday's poll which sent opposition Syriza into a tailspin after taking 20.1% of the vote and tumbling more than 11 points since the last election in 2019.

A new electoral system means New Democracy fell just shy of an absolute majority, paving the way for coalition talks this week though a second vote in June is more likely.

But the outcome was still a surprise. Prime Minister Kyriakos Mitsotakis emerged stronger despite a wiretapping scandal, the COVID pandemic, a cost of living crisis and a deadly rail crash in February which triggered public outrage.

It was a stunning defeat for Syriza, whose style of a radical, anti-establishment movement opposed to all, had resonated with angry voters more than a decade ago when Greece was forced into bailouts.

Then leader Alexis Tsipras and his finance minister Yanis Varoufakis were global household names when Greece was racked with violent street protests against swingeing wage and pensions cuts imposed by the international community.

After winning the election in 2015, the grouping of Marxists, anti-capitalists, socialists held chaotic talks with lenders that almost cost Greece its place in the euro zone.

But since Greece's bailout programme ended in 2018, it has regained market access, wrestled down its record debt and growth is set to outpace the euro zone's average - and politics and public anger have quietened down as a result.

CRISIS ERA

Syriza lost power to New Democracy in 2019, but four years on, polling had showed it could still be a force to be reckoned with, especially against an incumbent government facing so many challenges, running just 4-7 points behind Mitsotakis' party.

"I think what Syriza missed was the willingness of the electorate to move away from the crisis politics era. That is what Mitsotakis understood whereas Syriza didn't," said Wolfango Piccoli, co-president of political risk advisory at Teneo.

While voters' priority was the economy and their pockets, Syriza focused on other issues.

Its rallying cry for the election was "We Know, We Can Bring Change" and "Justice everywhere". It had proposed policies it said would bring voters in from the far right.

Syriza also sent mixed signals on a potential coalition government with leftist parties, some set up by former disgruntled Syriza allies, which quickly rejected its proposal.

"The result means Syriza needs to redefine its strategies and tactics," said pollster Costas Panagopoulos from Alco. "It needs an agenda closer to society and the agenda it did have - wiretapping and the like, weren't in the public's priorities."

Syriza officials were deep in talks on Sunday and Monday on what went wrong.

"We did not convince people," a party insider told Reuters. "Our proposal for a progressive coalition government did not convince."

Another leftist party, MeRA25, led by Varoufakis, used a similarly cryptic slogan "Alliance for the Rupture". It did not gain a seat in Sunday's poll.

"People just want to turn the page, look at some sort of hope rather than the toxic politics of the last 10 years or so," Piccoli said.

(Editing by Alison Williams)