PASOK's Venizelos said he favors the formation of a unity government that is "EU-oriented, regardless of what their take is" on previously implemented measures. His party will have 41 seats in parliament, down from 160 before the elections.

The tribulations of New Democracy and PASOK were matched by triumphs of a number of other parties that were also-rans and in some cases nonexistent just a few years ago, propelled by voters angry about stringent austerity measures.

The radical leftist coalition Syriza passed PASOK with a strong second-place showing. Exit polls predicted it would garner 10% support, but instead Syriza garnered 16.7%, according to the results. That more than triples its parliamentary representation to 51 seats.

The fourth-place finisher, the Independent Greek party, was founded in February by ousted New Democracy member of parliament Panos Kammenos. With 10.6% backing, this right-wing nationalist party, which opposes Greece's agreement with the European Union and International Monetary Fund, will now have 33 seats in parliament.

The Communist Party, which wants Greece to leave the single-currency eurozone, also saw gains in winning 8.5% support.

And the far-right Golden Dawn party, which got 0.3% of votes in the previous election, ended up with 7% support on Sunday. That equates to a rise from zero to 21 parliamentary seats.

Its leader, Nikos Michaloliakos, gave a rousing speech after Sunday's vote, saying Golden Dawn will "fight so that Greece won't be a slave of the memorandum and of the social jungle that illegal immigrants have brought in this country."

"Everyone who betrays Hellenism should be afraid. We are coming," he said.

Katerina Sokou, financial editor of the Greek daily newspaper Kathimerini, called what happened Sunday "a protest vote (against) the main two political parties of Greece."

Yet Sokou added that she expects New Democracy and PASOK again will be part of the ruling coalition government, even though there may be notable policy changes and challenges to come, including a "renegotiation" of the already approved austerity measures.

"I believe that these electoral results ... show that people need a coalition government," she said. "They also want the parties to cooperate."