The Socialist Party of late Serbian strongman Slobodan Milosevic has emerged as a kingmaker, after an inconclusive presidential election in which voters punished the ruling Democratic Party for their economic woes.

Preliminary results released Monday show incumbent Boris Tadic of the Democratic Party, slightly ahead of his main challenger, Tomislav Nikolic of the nationalist Serbian Progressive Party.

Neither contender has even 30 percent of the vote, and a majority is necessary to win the election. So President Tadic and Mr. Nikolic will face off in a second-round vote on May 20.

The key to either's success will be to form an alliance with the Socialists.

While both candidates support Serbian membership in the European Union, Mr. Nikolic is seeking to take advantage of voter anger with the Serbian economy and its 24-percent unemployment.