PARIS - Candidates in France’s presidential election made last-ditch appeals to sway undecided voters on Thursday as the third and fourth placed contenders kept up the pressure on the two hopefuls leading opinion polls.

Voters will cast ballots on Sunday in the first round of what has turned into the most unpredictable French election in memory, with four of the 11 candidates within reach of the two places for the run-off on May 7.

Pollsters see centrist Emmanuel Macron and far-right Marine Le Pen taking the top two places on Sunday and so going head-to-head in the run-off. That would break the normal rotation of power in France between the centre-left and centre-right. Polls on the race to succeed the deeply unpopular socialist President Francois Hollande are so close that gaps between candidates fall within the margin of error.

A Harris Interactive poll showed Macron and Le Pen still in front, with the gap a bit wider than before. The centrist inched ahead to 24.5 percent while Le Pen was a bit weaker on 21 percent. Conservative former prime minister Francois Fillon scored 20 percent, meaning he was now gaining on Le Pen.

Jean-Luc Melenchon, a far left politician propelled from wildcard to genuine contender thanks to feisty television performances and smart social media campaign, was stable on 19 percent. An Ifop-Fiducial poll showed roughly the same breakdown.

All 11 candidates fielded questions on television about their policies on Thursday evening, the last real chance in the election spotlight for some of them after a tumultuous campaign of surprises and scandal. The election will decide the direction of France’s 2.2 trillion euro economy, which vies with Britain for the rank of fifth largest in the world. With eurospectics Le Pen and Melenchon in the race, the outcome could have a bearing on France’s place in Europe.

The outcome will be watched closely by France’s allies given its role as a nuclear-armed permanent veto-wielding member of the UN Security Council and its military and diplomatic clout in the Middle East and West Africa.

Macron, a former banker who quit as economy minister last August to set up his independent “En Marche!” (“Onwards!”) movement, would beat Le Pen or any other candidate in the run-off, the Harris poll showed, echoing other polls.

On Thursday evening, Macron won the support of former prime minister Dominique de Villepin, a conservative Gaullist who won global celebrity by dramatically opposing US plans for war in Iraq.

Fillon, 63, was seen to be on an easy ride to the Elysee Palace at the beginning of the year but his campaign hit the rocks following nepotism allegations that he has denied.

His ratings have gradually recovered and on Thursday he redoubled attempts to dissuade his core voters from straying to Macron’s camp.

Seizing on a foiled attack this week in which he and other candidates were seen as potential targets, Fillon sought to reinforce his credentials as a strong pair of hands on security.

“In the fight against militants, like on everything else, Emmanuel Macron’s stance is blurry,” Fillon told Le Figaro newspaper, adding he would take a much harder line with extremists.

Melenchon, in an interview with BFM TV, pressed his criticism of European Union institutions - a position that has increasingly worried investors as his support has grown.

He said France needed to use its influence to push through pro-growth reforms and renegotiate EU treaties.

“I want people to know, for all of Europe to hear clearly, that this needs to change or it’s not going to go on like this, it’s not possible,” Melenchon said.

His “plan B”, should reform discussions fail, would be to put France’s exit from the EU to a referendum just as Britain did last summer.

“People often say I’m the one putting Europe at risk, that I want to leave. Listen - it’s not me putting Europe at risk, I didn’t make the British leave ... and we too are fed up.”

The prospect of Melenchon or Le Pen, whose more strident anti-EU stance includes dumping the euro currency, reaching the run-off - or, even worse, both of them - has put pressure on French bond yields.

French 10-year bond yields fell briefly to a three-month low earlier on Thursday, though, as polls showed some stability.