Hugo Chávez was re-elected Venezuela's president for a six-year term on Sunday with 61 per cent of the vote, 23 percentage points ahead of his main opponent, who conceded defeat but challenged the magnitude of the margin.
Manuel Rosales, the predominant opposition candidate, won about 38 per cent of the vote, according to preliminary official results based on a tally from 78 per cent of polling stations, the National Electoral Council said.
Mr Chávez's 23-point lead - if an audit comparing electronic voting results with paper records confirms the results - would be roughly in line with most opinion polls published in the run-up to Sunday's ballot, which suggested he would win with a lead of around 20 points.
An exit poll released early Sunday evening by US pollster Evans/McDonough had suggested Mr Chávez was leading with 58 per cent compared with 40 per cent for Mr Rosales.
Mr Chávez, a former army officer who often rails against the Bush administration and who has governed the world's fifth largest oil exporter for almost eight years, pledged to radicalise his left-leaning "Bolivarian Revolution".
"Today begins a new era," screamed Mr Chávez, a close ally of Cuba's ailing president Fidel Castro, during his victory speech from a balcony at the presidential palace in Caracas. "The central idea of that new era will be the deepening and the expansion of the Bolivarian Revolution towards Socialism."
Mr Rosales, who stepped down as governor of the western oil-rich state of Zulia barely four months ago to challenge the incumbent, on Sunday night conceded defeat but vowed to continue battling for an alternative model to Mr Chávez's militaristic blueprint for the country's development.
Earlier in the day he said that "problems" were delaying voting in as many as a third of polling stations, and he alleged that voters who claimed they had voted for him received "null vote" paper receipts from electronic voting machines, which have been plagued by technical glitches in previous votes in Venezuela.
Mr Rosales on Sunday night insisted that, after studying the results of two exit polls commissioned by his campaign and four "quick counts", Mr Chávez's margin of victory was "much smaller" than the partial results indicated.
"I speak as a democrat but also as a fighter," Mr Rosales said. "This was a tough battle against unfair advantage and all the structures of the state combined. But we are not stupid. The margin was much smaller than this."
Mr Rosales rebuffed calls from radical opponents appealing for him to forcefully challenge the results and organise protests, marking distance from previous, and failed, efforts by opposition leaders to win power on the streets.
Earlier in the evening, other opposition spokesmen had alleged that voting centres had been re-opened in some areas to allow hastily mobilised presumed pro-Chávez supporters to vote, an allegation denied by the government.
Before the partial result was announced, Teodoro Petkoff, a leading political commentator and Mr Rosales's chief campaign strategist, urged opponents to be patient for the result of the auditing process, which was expected to take several hours.
Electoral witnesses and some international observers from the Organisation of American States and other institutions were due to oversee the audit of electronic ballot results at about 17,500, or 54 per cent, of polling stations.
Nevertheless, shortly after the partial election results were announced, Mr Chávez celebrated by singing the national anthem before hundreds of cheering supporters who had amassed near the palace.
Government supporters set off a volley of fireworks in the centre of the city and in the poor slums that encircle the city, home to Mr Chávez's political constituency.
During the day, Mr Chávez, who likes to portray himself as the voice of not only the Venezuelan poor, but also of the downtrodden around Latin America, turned up to vote in a poor neighbourhood of Caracas driving a red Volkswagen Beetle.