Voters narrowly rejected the proposed constitutional changes in Sunday’s vote, an unprecedented defeat for a leader accustomed to landslides.

After a night of political drama, election officials announced the Opposition had won 51% and the government 49%, a result that slammed the brakes on Chavez’s self-styled revolution. Opposition supporters set off fireworks and poured on to the streets to celebrate what they said was the preservation of democracy from a power-hungry autocrat.

The rebuff will oblige Chavez to stand down when his term ends in 2013 rather than continuing to run for office until 2050 as he had hoped. It will also embolden the opposition and open fissures within his movement now that he has proven politically mortal.

The president conceded defeat in a televised broadcast minutes after the result was announced at 1:20 am Venezuelan time (5:20 am GMT). “This was a photo finish,” he said. The margin was “microscopic” but he would respect the will of the majority.

“I congratulate you,” Chavez said calmly, referring to his opponents.

The former soldier said he would continue his battle to build socialism and that the proposed changes had failed “for now” but were “still alive”, suggesting he may try to revive them later.

The conciliatory tone was a sharp contrast to his campaign rhetoric, which denounced his opponents as “fascists”, “traitors” and “mental retards”. Sceptics said the president played the role of dignified democrat only after frantic backroom talks with senior aides and election officials that delayed the results for hours.