Related: Turnout Higher in Serbia's Presidential Election

Serbia's incumbent President Boris Tadic won 50.5 percent or some 2.28 million votes in the tightly- contested presidential run-off on Sunday, defeating his rival Tomislav Nikolic, said preliminary results.

Nikolic of the Serbian Radical Party gained 47.9 percent or 2. 18 million votes in the run-off, said the Center for Free and Democratic Elections (CeSID), a local leading pollster.

Tadic of the Democratic Party told a press conference that it was a common victory and congratulated all the citizens of Serbia who "have showed that Serbia is a great European democracy."

He congratulated his contestant Nikolic on "a very difficult and fair fight."

Meanwhile, Nikolic acknowledged electoral defeat and congratulated Tadic.

He said at a press conference that Tadic, in all likelihood, has won in the second round and that the difference between the two was around 2 percentages.

Jubilant Tadic supporters poured onto the streets in downtown Belgrade, sounding car horns and waving blue and yellow Democratic Party flags as they drove around the downtown area. Thousands gathered in the main Republic Square, where Tadic held his final election rally, while others converged on the party's headquarters.