Opposition leader Tomislav Nikolic, a former ultra-nationalist last in power when Serbia was bombed by Nato in 1999, declared victory in a presidential run-off on Sunday and pledged to keep the Balkan country moving towards the European Union.
Based on an unofficial projection, Nikolic narrowly beat liberal incumbent Boris Tadic, who quickly conceded defeat after eight years as president.
Addressing concern in the West and the region over his past as an ally of late Serb strongman Slobodan Milosevic, Nikolic said in his first comments that Serbia "will not stray from its European path."
"This was not a referendum for or against the EU, but to resolve internal problems that were created by Tadic and the Democratic Party," he said.
"We must start to work, to rid ourselves of crime, to solve the political oligarchy and seek friends the whole world over."
Based on a sample count, pollster CESID put Nikolic ahead with 49.8% against Tadic on 47% after a run-off in which fewer than half of Serbia's eligible voters turned out.
A Nikolic victory could potentially split power in the former Yugoslav republic, with Tadic's Democratic Party poised to again lead the government in a coalition after a May 6 parliamentary election.
Under the Serbian constitution, the prime minister is more powerful than the president, but the head of state can hold up legislation.
Tadic called on the country to stick to its EU path, having become an official candidate for membership of the bloc in March.
"I am appealing to all political factors to preserve Serbia's strategic orientation towards the EU," he told a news conference.
Twice elected president since 2004, Tadic, 54, was part of the reformist bloc led by the liberal Democratic Party that ousted Milosevic in 2000 after a decade of war and isolation during the collapse of Yugoslavia.
He steered Serbia towards integration with the EU, but there is deep frustration among Serbs over the grinding transition from socialism to capitalism and an economic slowdown that has driven unemployment up to 24%.
"For the last eight years I was responsible for every human life, for every lost job, and it wasn't easy," Tadic said.
As deputy leader of the ultranationalist Radical Party, Nikolic, 60, was in government with Milosevic when Nato bombed Serbia for 11 weeks in 1999 to halt the massacre and expulsion of ethnic Albanians by Serb forces.
But since losing to Tadic in 2008 and forming his own Serbian Progressive Party, Nikolic has tried to rebrand himself from ultranationalist to pro-European conservative, and accused his opponent of presiding over a creeping culture of elitism.
The West has been encouraged by Nikolic's apparent conversion to the ultimate goal of EU membership, but Western diplomats say they remain unsure about the actual substance of his policy.
Both Nikolic and Tadic say they will never recognise Serbia's former Kosovo province as independent.
Nikolic's straight-talking, man-of-the-people manner appeals to rural Serbs and ordinary voters struggling with an average net wage of 380 euros ($480) per month.
"After all the unfulfilled promises and corruption under Tadic, I believe Serbia needs to be refreshed and that's why I voted for Nikolic," said Miodrag Petrovic, a 38-year-old marketing executive.
Tadic began the day as the frontrunner, but analysts had said a low turnout might favour Nikolic, whose supporters are considered more disciplined voters.
"This is the first time in 25 years that I've decided not to vote," said 44-year-old Belgrade engineer Zoran Momirov.
"I'm deeply unhappy with Tadic's policies and the nepotism and corruption of the Democrats and their clique, but I'm equally unhappy with whatever Nikolic has to offer."