PARIS  - French President Nicolas Sarkozy hunted for far-right votes Monday after losing to Socialist Francois Hollande in a first round vote that saw a shock breakthrough by the anti-immigrant National Front.

The right-wing incumbent moved quickly to woo the 18 percent of voters who backed the Front’s Marine Le Pen, saying they deserved an answer to their concerns, as German Chancellor Angela Merkel called her showing “alarming”.

Hollande and Sarkozy are to face each other in a run-off on May 6 after Sunday’s first round saw the Socialist beat the incumbent by a vote of 28.63 to 27.18 percent, according to final official results.

Hollande’s victory cemented his position as the clear leader in the race, dealing a blow to Sarkozy’s hopes of gaining enough momentum from a first-round win to defy expectations and return to office. But it was the showing of populist nationalist flagbearer Le Pen that shook up the race, setting up her National Front (FN) voters as potential kingmakers. “We must respect the voters’ will, it is our duty to listen,” Sarkozy told journalists before going back on the campaign trail in the Loire Valley in central France.

“There was this crisis vote that doubled from one election to another, an answer must be given.” Le Pen’s score on Sunday was nearly double the 10.4 percent her father Jean-Marie took as the FN candidate in the 2007 first round.

Hollande resumed campaigning with a trip to the western region of Brittany, where he said that the FN’s first round score reflected anger in the country and that he would also listen to far-right supporters.

“Nicolas Sarkozy is to blame for the far-right’s high level,” he said earlier before leaving Paris. “There are voters who may have been been led to this through anger. That is what I want to hear.”

Polls show most far-right supporters prefer Sarkozy but up to a quarter - mainly working-class voters attracted by Le Pen’s protectionist trade policies - could switch to Hollande.

Le Pen’s high score stunned observers and she told supporters after the results that “the battle of France has just begun” and “nothing will be as it was before.”

In the first foreign reaction to the result, Merkel’s spokesman said: “This high score (for Le Pen) is alarming but I expect it will be ironed out in the second round.” Sarkozy, who had already swung to the right in the campaign, brandished his right-wing credentials in his first post-results speech on Sunday.

“These anxieties, this suffering, I know them, I understand them,” he said.”They are about respecting our borders, the determined fight against job relocation, controlling immigration, putting value on work, on security.”

The first opinion poll after the first round said that Hollande would beat Sarkozy by 54 percent to 46 in the second round.

Analysts say it is extremely unlikely Le Pen will endorse either candidate in the second round but she has said she will express an opinion on May 1 - a week before the run-off.

Sarkozy, whose camp believes he is a stronger personal campaigner than Hollande, went on the offensive Monday with a challenge to the Socialist not to refuse his proposal for three televised debates before the second round.

“This is about debating before the French people, project against project, personality against personality, experience against experience. The French people have a right to know, Mr. Hollande must not run away.”

Sarkozy has challenged Hollande to three televised debates, but the frontrunner insists one would be enough.

“This is a crucial moment, the French people must have all the facts to make a choice. I will not run away, I will not hide and if Mr Hollande hides, that will be his responsibility,” Sarkozy said.

The left has not won a presidential election in a quarter of a century, but with France mired in low growth and rising joblessness, opinion polls had long predicted Hollande would beat Sarkozy.

Hollande says Sarkozy has trapped France in a downward spiral of austerity and job losses, while Sarkozy says his rival is inexperienced and weak-willed and would spark financial panic through reckless spending pledges.

Europe’s main stock markets fell sharply as traders reacted to the results, as well as to Chinese manufacturing data and persistent eurozone debt tensions.