Nationalist candidate Tomislav Nikolic won the Serbian presidency, a result that adds to the political turmoil in the Balkan country and could slow down its attempts to join the European Union.
The Centre for Free Elections and Democracy, an independent polling group, said today that Mr Nikolic won 49.4% of the vote, while pro-European Union incumbent Boris Tadic received 47.4%.
Mr Tadic conceded defeat, saying: "I wish Nikolic the best of luck." The results are expected to be officially confirmed later.
The outcome was a sign of the fading allure of the EU, which is plagued by a debt crisis, and voter discontent with Serbia's weak economy.
Mr Nikolic must name a prime minister, but that task has been complicated because of the outcome of the May 6 parliamentary election.
Although Mr Nikolic's Progressive Party won the most seats, Mr Tadic's Democrats have tentatively agreed on an alliance with Socialists that would give them a majority. Mr Nikolic has claimed the May 6 vote was marred by fraud.
"We'll see what will happen," Mr Nikolic said as his supporters chanted his nickname, Tomo the Serb, on the main squares in Serbian cities.
The outcome also could hugely impact Serbia's plans to become an EU member, a major step for a country that was a pariah state under late autocrat Slobodan Milosevic in the 1990s.
It also could determine whether Serbia continues to reconcile with its neighbours and wartime foes, including the former province of Kosovo, which declared independence in 2008. Serbia has refused to recognise Kosovo's independence.
Mr Nikolic, who narrowly lost two earlier presidential votes to Mr Tadic, claimed to have shifted from being staunchly anti-Western to pro-EU.