Leftist former diplomat Danilo Tuerk is set to become Slovenia's new president, as preliminary results suggest he has a huge lead over his centre-right rival.
Mr Tuerk ran as an independent but was backed by the left-wing parties
Former prime minister Lojze Peterle conceded after exit polls showed Mr Tuerk getting almost 70% of the vote.
Mr Peterle - who helped lead Slovenia to independence from Yugoslavia - was well behind despite topping a first-round vote last month.
Mr Tuerk, 55, was backed by the main left-wing opposition parties.
Mr Peterle had the support of the governing centre-right coalition.
But the 59-year-old did not secure enough support to win outright in October, and has since fallen behind in the polls.
Mr Peterle conceded almost immediately. "I expected a better result," he said.
"I sincerely congratulate Danilo Tuerk on his victory. I wish him good luck in leading the country in the challenging times ahead of us."
Analysts say his defeat will come as a new blow for the administration after its poor performance in local elections last year.
Mr Tuerk is a long-time diplomat who gained a clear lead over his rival since he gathered support from backers of a leftist candidate who lost last month.
He said he was "very pleased with the results that are being forecast", although he pointed out they were not final.
"I believe the situation here is such that many citizens want something new, that wish is very strong and the campaign has been proving that wish all along," he added.
Mr Tuerk looks set to follow two other centre-left presidents - Milan Kucan, who served two terms from 1992 to 2002, and outgoing President Janez Drnovsek, who decided not to seek a second five-year term.
Mr Tuerk is not expected to change the alliances of the ex-communist state of two million people with Europe and Washington.
The role of president is largely ceremonial, but carries authority in defence and foreign affairs.
The new president will be sworn in shortly before Slovenia assumes the EU presidency on 1 January.