Serbian President Aleksandar Vucic has claimed victory in snap parliamentary elections, saying his party is heading for an absolute majority.
His Serbian Progressive Party, or SNS, is set to win almost 47% of the vote, according to projections.
Opposition parties under the Serbia Against Violence banner were well behind with 23.1%.
Their biggest hope is in challenging the president's party in Belgrade in Sunday's local elections.
Results overnight from Serbia's 8,273 polling stations confirmed the ruling party's lead, although projections in the capital itself gave it a far narrower margin of victory of four points.
Mr Vucic declared that his "Serbia must not stop" election list was heading for 127 seats in the 250-seat National Assembly.
"My job was to do everything in my power to secure an absolute majority," he told supporters, although he himself was not running for election.
Wearing a grey sweater, he was flanked on one side by Prime Minister Ana Brnabic and on the other by controversial Bosnian Serb leader Milorad Dodik.
Ms Brnabic had earlier brushed off reports of election irregularities at a number of polling stations in Serbia by non-government observers. She said they were aimed at "creating an atmosphere to cause chaos, panic and mistrust". Opposition parties referred to the electoral process as dirty.
The SNS has been in power since 2012 but there have been three elections in the past three years. As well as voting for parliament, Serbians were deciding on Sunday who would control 65 local authorities.
The loose opposition Serbia Against Violence alliance, or SPN, was formed after two mass shootings in May which sparked huge protests. The attacks killed 19 people, including 10 at a school in Belgrade.
The protests grew into demonstrations against President Vucic and his SNS party.
Opposition parties said the massacres reflected a culture of rhetorical and physical violence promoted by the ruling party and its allies in the media.
As the projected results began to filter through late on Sunday night, the mood at one of the parties in the Serbia Against Violence coalition was uncertain.
If supporters of the Green-Left Front had been hoping for a major swing away from the president's Progressive Party, they soon realised that was not going to happen.
There were a few catcalls from activists as the prime minister appeared on a screen to claim victory, rejecting claims of irregularities as "untruths, insinuations, unverified information and fake news".
But opposition candidates for Belgrade city council at the post-poll event remained optimistic that they could still gain seats and prevent the Progressives from retaining control of the capital.
Almost one in four Serbian voters lives in Belgrade, so any dent in the profile of the president's party there would count as a success.
Earlier a former Belgrade mayor, Dragan Djilas, who is also a leader of the Serbia Against Violence coalition, told reporters that "changes in Serbia have begun".
He suggested that people were determined to live "normally without crime and corruption, without prices going wild". Serbia is struggling with high inflation, which hit 8% in November.
But President Vucic told supporters that the party had seen off the opposition challenge in Belgrade and that he was confident the capital would once again be run by former water polo star Aleksandar Sapic, who merged his party with the Progressives.
A projection by CeSID/Ipsos early on Monday gave the Progressives 48 seats in Belgrade to the opposition's 43.
Mr Sapic, who appeared on stage with the president, said the opposition had been claiming for a year that Belgrade was theirs, and where the change of power would begin: "And we won again in Belgrade."
Opposition figures have accused the SNS of using public resources for political purposes and election monitor CRTA complained before the vote of a "chronic lack of pluralism" in Serbia.
Turnout nationally was estimated at 59.1%.
Local observers reported various irregularities on Sunday, including voters being bussed in from Bosnia-Herzegovina to vote in Belgrade.
The CRTA observer mission gave details of attempted ballot-rigging in a number of polling stations.
Serbia is a candidate to become a member of the European Union, and President Vucic is under pressure from both the EU and the US to normalise relations with Kosovo.
Kosovo declared unilateral independence from Serbia in 2008, and while it is recognised by more than 100 UN members, Serbia has refused to do so - backed by allies like Russia, China and five EU members.
Some 95,000 ethnic Serbs live in Kosovo and those who wanted to vote had to cross into Serbia to cast their ballot.
