Greece's charismatic radical left leader Alexis Tsipras appears on track for a second mandate as premier of the crisis-hit nation after a tense election race against his mainstream conservative rivals.
With more than a quarter of the votes counted on Sunday (local time), the Syriza party had a larger-than-expected lead of 35 percent against 28 percent for the conservatives.
This led the leader of the conservative New Democracy party, Vangelis Meimarakis, to admit defeat.
"It appears that Mr Tsipras' Syriza is first, I congratulate him," he said.
At Syriza party headquarters, Tsipras was greeted with a huge round of applause by supporters who clapped and shouted when the results of the exit polls were announced, breaking into Italy's revolutionary anthem, Bandiera Rossa, Italian for "Red Flag".
Tsipras earlier on Sunday declared he was confident of winning a second mandate to reform and revive the nation's economy after a first tumultuous seven months in power.
Wearing his trademark open shirt and cheery smile, he said after casting his ballot that voters will elect "a fighting government" ready for the "confrontations necessary to move forward with reforms".
Hands-down winner of a January general election, then with 36.34 percent of the vote, Tsipras resigned in August and called snap elections, gambling crisis-weary Greeks would give him a new mandate despite his controversial austerity deal with European leaders.
After winning office on an anti-austerity ticket, he agreed in July to more punishing austerity for the nation in exchange for its third financial rescue in five years.
He later argued he had effectively saved Greece from a chaotic exit from the eurozone.
The move alienated many Syriza supporters and split the party, with a fifth of its anti-euro hardline MPs walking out, forcing Tsipras to call the election.
He went to the polls facing a strong challenge from the conservative New Democracy party led by ex-defence minister Meimarakis, who slammed the former leftwing premier for his U-turn with the country's creditors and for his seven chaotic months in power.