A pro-Western reformer defeated a hard-line nationalist ally of Slobodan Milosevic in a runoff election for Serbia's president Sunday, the state electoral commission said.

Boris Tadic received 54 percent of the vote, while Tomislav Nikolic got 45 percent.

The presidential vote was seen as crucial to deciding whether Serbia moves closer to the European Union and NATO or sinks back into the nationalist isolation reminiscent of Milosevic's autocratic rule.

"This election has shown that Serbia knows how to recognize a historic moment," Tadic said, celebrating his victory.

"My hope is that Serbia will never again be led by a man who will spearhead the killing of our countrymen," he added, referring to Milosevic, whose government triggered the Balkan wars of the 1990s that broke apart Yugoslavia.

Three previous attempts to elect a president since 2002 failed because too few voters showed up at the polls. This vote was certain to produce a president regardless of the turnout -- 48 percent of those eligible participated -- after Parliament scrapped a 50 percent requirement.

The turnout was about the same as in the first round of voting two weeks ago. Since then, however, Prime Minister Vojislav Kostunica, most ethnic minorities and dozens of local celebrities have tried to rally support for Tadic, who was among 14 candidates in the first round.

Tadic has been an ardent supporter of extraditing Serbian war crimes suspects to the U.N. war tribunal in The Hague, where Milosevic and others are standing trial on charges related to their roles in the Balkan wars in the 1990s -- Europe's worst carnage since World War II.

Nikolic, 52, strongly opposes Western extradition demands and had said he would dedicate a victory in the election to Milosevic.

Tadic, 46, a soft-spoken psychologist and college professor born in the Bosnian capital, Sarajevo, entered politics in 1990 as a member of the pro-Western Democratic Party.

After the March 2003 assassination of Zoran Djindjic -- the Democrats' leader and Serbia's first noncommunist prime minister since World War II -- Tadic was catapulted to the forefront, taking the party helm this past February.

Runoff winner Boris Tadic greets supporters after receiving 53.5 percent of the vote.