French President Nicolas Sarkozy made a last-ditch appeal to far-right voters on Thursday after failing to land a knockout blow in a heated televised debate with Socialist rival Francois Hollande before Sunday's decisive runoff.

Hollande, ahead in opinion polls by six to 10 points, was calm and unflappable during the nearly three-hour debate on Wednesday while the conservative Sarkozy, struggling to catch up with the moderate social democrat, was often agitated and tense.

Commentators said the confrontation, watched by 17.8 million people out of an electorate of 44.5 million, was no game-changer and probably only reinforced voters' opinions in a contest that has been as much about style and personality as substance.

"It was a draw but as Mr Hollande started as favourite, he remains the favourite," wrote Francoise Fressoz in an editorial in Le Monde. "Mr Sarkozy did not manage to destabilise him, which was his objective from the start."

Returning to the airwaves on Thursday in a bid to convince waverers before campaigning ends at midnight on Friday, Sarkozy appealed to the nearly one-fifth of voters who cast their ballot for the National Front in the April 22 first round.

"The opinion polls are lying. An election has never been this open ... It's even more open after the debate," Sarkozy told RTL radio.

"I want to speak directly to National Front voters. Who would benefit if you cast a blank vote? It would benefit Hollande, the regularisation of (illegal) immigrants, crazy overspending."

Television commentators said Sarkozy had performed "like a boxer" in Wednesday's debate and Hollande "like a judo fighter", using flashes of wit and interjections to unbalance his rival.

"Hollande presides over the debate," left-wing Liberation wrote on its front page, while the right-leaning Le Figaro, with a headline "High Tension", emphasised the bitterness of the exchanges. It noted that every euro zone leader to seek re-election since 2008 had lost, but said divisions in the French left and Hollande's outdated policies gave Sarkozy a chance.

Hollande, 57, was confident and relaxed in the early exchanges of Wednesday's contest, saying he aimed to be "the president of justice" and "the president of unity".

He said Sarkozy, also 57 and in office since 2007, had divided the French people and was using the global economic crisis as an excuse for broken promises. "With you it's very simple: it's never your fault," Hollande said.

Sarkozy, fighting for his political life, repeatedly accused his opponent of lying about economic figures and reeled off reams of statistics in an attempt to swamp his adversary.

Deriding Hollande's pledge to be a "normal president", the president said: "Your normality is not up to the challenge."

The two sparred over Europe, which has become one of the biggest issues of the election race, as well as the sickly economy, 10 percent unemployment, nuclear power and immigration.

"The example I want to follow is Germany and not Spain or Greece," Sarkozy said, declaring that he and German Chancellor Angela Merkel had saved Greece from an economic wipeout and avoided the collapse of the euro currency.

"Europe has got over it," Sarkozy said of the crisis.

Hollande shot back: "Europe has not got over it. Europe is today facing a possible resurgence of the crisis with generalised austerity, and that's what I don't want."

The Socialist, who vowed to push for a new focus on growth to allow the euro zone to convalesce, said people across Europe were watching the election in the hope it would change the bloc's economic direction for the better.

Sarkozy, being punished for rife unemployment and a brash manner, is the most unpopular president to run for re-election. He was the first in recent history to lose a first-round vote, with Hollande benefiting from the anti-incumbent sentiment that has swept 11 euro zone leaders from office since 2009.

The streets of Paris were unusually deserted with many people staying home to watch the debate, although some chose to follow the clash on television screens at their local cafe.

"It has been 50-50. There is no clear winner," said Jacques Dufoix, 36, a computer engineer, after watching the debate in a central Paris sports bar. "I don't think this is going to change the way anyone votes. People have already made up their minds."

A handful of opinion polls due to land before Friday evening will measure any impact.

Sarkozy suffered a setback this week when far-right leader Marine Le Pen - whose 17.9 percent score was the surprise of the first round - refused to endorse him. She vowed at a Paris rally on Tuesday to cast a blank vote and told supporters to make their own choice, focusing most of her attacks on Sarkozy.

The issue of how to deal with the anti-immigration crusader and her agenda has tormented Sarkozy's UMP party all week, as a TNS Sofres opinion poll found a third of voters agreed with the National Front's positions.

The candidates tangled on immigration in the debate, with Sarkozy attacking Hollande's proposal to give long-term, non-European foreign residents the right to vote in local elections.

Sarkozy began campaigning weeks after the more plodding Hollande, vowing to boost industrial competitiveness, hold referendums on contentious policies, crack down on tax exiles and make the unemployed retrain before receiving benefits.

More recently, seeking to court the 6.4 million National Front voters, he has vowed to cut immigration and threatened to pull out of Europe's Schengen zone of passport-free travel unless the European Union's external borders are strengthened.