Nikolic has also made it clear that he would be unlikely to press for efforts to find Gen. Ratko Mladic, wanted at the Hague for war crimes for the Srebrenica massacre. The EU has declared that if Serbia wants to continue to move toward membership, Mladic must be found.
When Nikolic and Tadic faced a similar scenario in the 2004 elections, the country chose to go with the pro-Western candidate. But that was then and this is now, experts say.
Since 2004, Serbia's political and emotional mood has shifted to the right, favoring nationalists like Nikolic, who advanced to the runoff by receiving 40 percent of the first round vote. Tadic received 35.4 percent.
Marko Blagojevic from the Center for Free Elections and Democracy told ABC News that Tadic "has a slight advantage," but the gap falls within the range of a statistical error.
"A few tens of thousands votes -- we might have Florida," he said, referring to disputed vote in the 2000 presidential race.
The divisive election is expected to encourage an unusually high turnout of around 65 percent out of 6.7 million eligible voters, he said.
The president, although largely a ceremonial position, is the head of the armed services, making it more important than the job description. And electing the president has become a barometer of popular -- and thus political -- sentiment.
As the leader of the large party in government with prime minister Vojislav Kostunica, Tadic has a great deal of influence.
Nikolic, on the other hand, is the acting leader of the largest party in parliament.
The choice Serbs face Sunday is seen by many experts as a crucial one not just for their country but for people across the Balkans who fear another decade of instability and economic stagnation.