Tsipras sworn as first left prime minister of Greece

Within hours of victory on a campaign of "Hope is coming!", the 40-year-old Tsipras sealed a coalition deal with the small Independent Greeks party which also opposes Greece's EU/IMF aid programme though the two parties are at odds on many social issues like illegal immigration.

The alliance is an unusual one between parties on the opposite end of the political spectrum brought together by a mutual hatred of the 240-billion-euro bailout programme keeping Greece afloat at the price of budget cuts.

The alliance suggests a hardline stance against Greece's creditors, who have dismissed Tsipras's demands for a debt write-off and insisted the country stay on the path of reforms and austerity to get its finances back on track.

Yanis Varoufakis, an outspoken crusader against austerity, an economist teaching in the US and a blogger, was expected to become finance minister when the cabinet is unveiled on Tuesday, senior party officials said.

"The people of Greece gave a vote of confidence to hope," economist Varoufakis wrote on his blog. "They used the ballot box, in this splendid celebration of democracy, to put an end to a self-reinforcing crisis that produces indignity in Greece and feeds Europe's darkest forces."

Reaction from financial markets to SYRIZA's victory was largely muted, with the euro recovering from a tumble to an 11-year low against the dollar on initial results. Greek stocks fell 2.7% while 10-year bond yields rose but stayed below the levels seen in the run-up to the vote.

For the first time in more than 40 years, neither the New Democracy party of Samaras nor the center-left socialist PASOK, the two forces that had dominated Greek politics since the fall of a military junta in 1974, will be in power, beaten by a party that has until recently always been at the fringe.

Tsipras also intends to talk to the heads of two other parties, the centrist The River and the Communist party to seek outside support for his coalition.

Together with last week's decision by the ECB to pump billions of euros into the euro zone's flagging economy despite objections from Germany, SYRIZA's victory marks a turning point in the long euro zone crisis.

It signals a move away from the budgetary rigor championed by Germany as the accepted approach to dealing with troubled economies, though it is unclear the extent to which SYRIZA will be able to wring concessions and aid from creditors.

But after the euphoria of election night Tsipras faces daunting challenges and can expect strong resistance to his demands from Germany in particular. A series of European policymakers urged SYRIZA not to renege on commitments.