In final voter surveys published 11 days ago, Berlusconi had a lead of between six and eight per cent.
By Italian law, no poll results can be published within 15 days of the vote.
Berlusconi, who has the distinction of having headed the only Italian government since World War II that lasted through a full five-year term, from 2001 to 2006, has been campaigning energetically in the run up to the vote.
His bid for power has been aided by his media empire that includes three of Italy's seven national television networks.
However, Veltroni, almost 20 years his junior, has also makes sophisticated use of the media, in stark contrast to Romano Prodi, the outgoing prime minister.
Marco Tarchi, a political scientist at the University of Florence, said: "Prodi's idea of politics was more ascetic. With Veltroni, the left has embraced marketing."
Veltroni and Berlusconi have similar platforms, with both pledging tax cuts and reduced government spending.
Tarchi said the two "are banking on image and television, there's no debate of ideas."
Whoever wins will have to contend with a stalling economy, a populace disaffected with the political class and more legislative gridlock.
Veltroni, a former journalist who created the Rome film festival in 2006 to wide acclaim, was Rome's mayor for seven years until he resigned to run in the elections.
Berlusconi's brand of populism, projected through his domination of the airwaves, propelled him to the premiership in 1994 aged 55, though his first stint lasted only seven months.
Despite a string of corruption investigations, he has sought to cultivate a "father of the nation" image.
In contrast, Veltroni is seeking to rejuvenate the political class and double the number of women in parliament.
The drive has spurred an unprecedented number of up-and-coming women to run in the elections to replace a parliament that is 84 per cent male.