The Socialist-controlled Belgrade electoral commission said that the Socialist party and its allies had won 66 out of 110 seats with only 32 seats going to the main opposition movement, Zajedno ("Together").
The announcement followed the Supreme Court's rejection of an opposition appeal against vote-rigging.
Within hours, thousands of students and other anti- government protesters were marching in central Belgrade and the Zajedno coalition vowed to prolong the three-week-old street demonstrations until President Slobodan Milosevic lost power.
Opposition leaders were clearly taken aback by the court's decision, which followed several signals from the authorities last week that they wanted to take the heat out of the crisis. Vuk Draskovic, one of Zajedno's three main leaders, said he feared Mr Milosevic was trying to goad the opposition into abandoning its peaceful methods of protest.
"I am expecting that tomorrow, the day after tomorrow, sometime soon, Milosevic will use police, maybe even the army, but we will not stop," he said. "He can arrest all of us, all of Serbia, but the only person in prison will be himself."
However, an opposition political adviser, Milan Bozic, said that Mr Milosevic was more likely to try to grind down the opposition without force.
By rejecting opposition demands that their victory in last month's municipal elections in Belgrade should be upheld, Mr Milosevic seems certain to incur still more criticism from Western governments.
They say the verdict of the electorate in Belgrade, and in 14 other large towns where the opposition defeated the ruling Socialists, must be respected if Serbia wants to return to inter- national respectability. In particular, the EU will continue to deny Serbia preferential trade terms, and Mr Milosevic will not have access to international credit, essential to hauling Serbia out of its economic mess.
The electoral commission's announcement appeared to greatly reduce the prospect that Mr Milosevic might eventually acknowledge the opposition's electoral victory in Belgrade. The Supreme Court had earlier decided that in 5 out of 46 electoral seats under review, opposition victories had been justifiably annulled.
Lawyers for the opposition said this decision indicated that the same ruling would apply to the other 41 seats. However, even the loss of five seats would have been enough to deprive the opposition of an overall majority in the 110-seat city council, since the total number of seats under its control would have fallen from 60 to 55.
The court's ruling bore all the hallmarks of a classic Milosevic ploy. For the court had dangled the prospect before the opposition of having exactly half the seats in Belgrade's city council and thereby acquiring just a taste of political power for the first time in Serbia since 1945.
At the same time, by switching the focus to the obscure legal processes of the Supreme Court, Mr Milosevic tried to divert attention from the central issue: whether he should remain in power. The opposition had hoped that, by winning recognition of its municipal election victories, it could build a platform for challenging Mr Milosevic in national polls next year.
However, the electoral commission's announcement suggests the President will never let the opposition come to power through the ballot box.