Tadic, leader of the Democratic Party, won yesterday's runoff ballot with 1.7 million votes compared to 1.4 million votes for Nikolic -- a margin of about 53.7 percent to 45.1 percent. Tadic said his five-year mandate will be defined by a reform agenda that prepares the country for European Union membership.
"I really believe that we will have a new political style in our country and I really believe that these elections are very important in terms of new political values in Serbia. I'm a candidate who is a pro-European candidate. That means that I'm for new political values here," Tadic said.
Analysts agree that Tadic's victory over Nikolic gives Serbia fresh resolve to carry out reforms that began nearly four years ago with the ouster of former Yugoslav President Slobodan Milosevic. Since then, reforms have become stalled by internal disputes that broke up the anti-Milosevic opposition.
In trying to predict whether reforms now have a better chance of being implemented, analysts in Belgrade say they are now monitoring the relationship between Tadic and Serbian Prime Minister Vojislav Kostunica, who heads a cabinet supported by a minority coalition in parliament.
In fact, Tadic's Democratic Party had been locked in a destructive power struggle with Kostunica's Democratic Party of Serbia for years.
Kostunica took a major step toward reconciling those differences when he publicly supported Tadic's campaign in the second round of the presidential poll. But key policy differences remain -- such as their positions on cooperation with the International Criminal Tribunal for the former Yugoslavia in The Hague.
Kostunica has said cooperating with The Hague is not one of his priorities. Tadic says such cooperation is a must, even if many Serbs think it dishonorable to hand over generals to what they believe is a biased court.
Serbian political analyst Djordje Vukadinovic, a researcher at the University of Belgrade, said the real test of the Tadic-Kostunica relationship rests on whether Tadic's Democratic Party attempts to strengthen its power base in parliament by calling for early general elections.
"I'm sure that in the initial period, the Democratic Party and Tadic will not directly and aggressively try to capitalize on this victory [by trying to call early parliamentary elections]. Since we have had a dilemma about whether [Serbia] will have a strong president or a weak president, I would say we have a moderately strong president. But [Kostunica's] government is even weaker than before the election. That [minority coalition] government was weak before the ballot because it was dependent upon the support of [Milosevic's] Socialist Party of Serbia. And from now on, I assume the cabinet will depend upon the support of [Tadic's] Democratic Party," Vukadinovic said.
Vladimir Goati, director of the Belgrade-based Institute for Social Sciences, told RFE/RL that he does not expect Tadic to push for early elections. "I can assume, based on the deeds and announcements of Mr. Tadic up to now, that he will not insist on early parliamentary elections," he said. "I think this tolerance of his is something fairly new in the political system of Serbia."
A senior official in Kostunica's Democratic Party of Serbia, Nebojsa Bakarec, told RFE/RL that he expects Tadic and Kostunica to work together on reforms rather than become embroiled in further disputes over the control of cabinet posts. "Boris Tadic announced that he will cooperate with the cabinet [of Kostunica], and the prime minister has [said he will cooperate with the presidency]," he said. "What is needed now is that we all push Serbia in the same direction so that we can accomplish the goal that is most important to our citizens -- to have a better life. I don't see any room for any political shakeups [in the cabinet]. I expect agreements and compromises."
Some Western officials had feared that divisions within Serbia's political center, combined with the assassination of reformist Prime Minister Zoran Djindjic in March 2003 and a nationalist backlash against reforms, might drag Serbia back into political isolation.
In his concession statement, Nikolic said that Tadic had won the ballot because of the votes of "ethnic minorities." Some analysts say those remarks are a sample of Nikolic's election-campaign rhetoric, along with his "dream of a Greater Serbia" that convinced rival parties to join together in support of Tadic.
When asked about the vitriolic remarks in Nikolic's concession speech, Tadic laughed with the smile of a victor: "My reaction is this -- who [becomes] the president of Serbia [is a question that] depends on our citizens. I don't make any difference between our citizens [on the basis of their ethnicity]."
(RFE/RL's South Slavic and Albanian Languages Service contributed to this report.)