Greeks angered by austerity take to the polls on Sunday for an election that could decide their future in the euro amid unprecedented external pressure not to vote for a radical leftist firebrand.
German Chancellor Angela Merkel said it was "extremely important" for Greeks to elect lawmakers who would respect the terms of a controversial bailout deal, which Syriza leader Alexis Tsipras has promised will be "history" on Monday.
Eurogroup chief Jean-Claude Juncker also warned on the eve of the vote that choosing Syriza could have "unpredictable" consequences for the eurozone as international markets watched the momentous vote with bated breath.
Polls open at 0400 GMT and close at 1600 GMT, with exit polls also due out then and the first indicative results expected at around 1900 GMT in the second election in six weeks after a vote on May 6 failed to produce a government.
Germany's Bild newspaper added to tensions ahead of the vote with an open letter telling Greeks their ATMs only had euros because "we put them there."
"If the parties who want to be through with austerity and reforms win the election and contravene every agreement, we will stop paying," it said.
Tsipras, a 37-year-old former student activist from a working-class Athens district, is running neck-and-neck in the polls with Harvard-educated Antonis Samaras, the 61-year-old head of the conservative New Democracy party.
"It's true we want to blow up a system that isn't working but I'm afraid Tsipras might turn out just as incapable as the others and that the situation might continue to get worse," said Dora Fotopoulou, a 48-year-old psychologist.
Tsipras argues that the mood in Europe is shifting against austerity and that the European Union and International Monetary Fund will not want to risk a Greek euro exit that would send shockwaves through the global economy.
At his final campaign rally, he accused Samaras of defending "Merkel's Europe of the past". "We guarantee the Europe of the future," he said.
Samaras wants a more moderate renegotiation of the bailout deal and warns that a vote for Tsipras could bring back the drachma currency.
Polls show an overwhelming majority of Greeks want to keep the euro.
"We will exit the crisis. We will not exit the euro. We will not let anyone take us out of Europe," Samaras said at his last election meeting.
In their public comments at least, European leaders warn that Greece must respect its international debt commitments or risk leaving the euro club, and the EU and the IMF have suspended loan payments until after the elections.
IMF chief Christine Lagarde told French daily Liberation talks with a new government must resume next week, saying: "We do not really know what has been implemented, what has been respected or not in the last six or eight weeks."
Greece has already been forced to seek bailouts twice, first for 110 billion euros in 2010 and then for 130 billion euros this year plus a 107-billion-euro private debt write-off -- for a total of 347 billion euros ($439 billion).
There have been suggestions that there is at least some room for compromise on the bailout conditions and a former Greek government adviser said a crucial deficit-cutting deadline could be extended to 2016 instead of 2014.
"There is always room for adjustment of terms," said former IMF economist Simon Johnson, a professor at the Massachusetts Institute of Technology in the United States.
"The question is whether the new government wants to negotiate in good faith and whether the European Union still wants to help. The IMF will do what it can, but the options are running out."
For many Greeks a fine-tuning of the terms of the loans may not be enough as public anger is rising against the steep pay and pension cuts seen since the crisis first exploded in 2009, setting off a chain reaction across Europe.
Greece is now in its fifth year of recession, and many young Greeks are voting with their feet by emigrating, while local media reports warn the state will run out of cash to pay public-sector salaries and pensions on July 20.
"We want the euro, but we also have to live. We can't sacrifice everything," said Syriza supporter Meri Primi, a 45-year-old teacher in Athens whose salary has fallen by 400 euros over the past two years to 1,100 euros a month.
No one party is expected to win enough votes to secure a majority in parliament, and the days to come are likely to be dominated by coalition talks.
Analysts say New Democracy would find it easier to form a coalition if it wins -- although it might struggle to secure a strong majority in parliament.
Syriza would find it harder to form a leftist coalition, analysts say.
"But both scenarios are not very easy," said Vassiliki Georgiadou, a political science lecturer at Panteion University in Athens.