PARIS (Reuters) - Former prime minister Francois Fillon is favorite to become the French center-right’s presidential candidate after a voting upset that puts him in pole position for a showdown with far right leader Marine Le Pen in next year’s election.

Fillon, who has said he will cut public sector jobs and rein in government spending, won 44 percent of votes in Sunday’s first-round of voting for the center-right’s nomination. He faces a second-round vote against another former prime minister, Alain Juppe, who trailed him by 15 percentage points.

Former President Nicolas Sarkozy came third and, after being eliminated, endorsed Fillon for the second-round vote next Sunday.

The outcome adds to uncertainty about the result of next year’s presidential election, likely to be decided in a runoff against the anti-immigration, eurosceptic National Front leader Le Pen in May. There is, though, no clear evidence Fillon would fare worse against her than would Juppe.

The only near certainty is that the deeply divided ruling Socialist Party is headed for a drubbing. Even so, some senior left-wingers expressed optimism that an eventual defeat for Juppe would open a space for them in the center.

The surprisingly big lead hands Fillon, 62, a strong advantage in the runoff. An admirer of late British Prime Minister Margaret Thatcher, he is probably the closest thing France has to an economic liberal and social conservative.

Although Fillon’s triumph on Sunday was a surprise, opinion pollsters had said he made a late surge in campaigning, and several stalwarts from the conservative Les Republicains party threw their weight behind him after his first-round success.

“I will vote for Francois Fillon because it is he who will best defend the values of the right,” said party president Laurent Wauquiez, a close Sarkozy ally.

A snap poll by Opinionway after Sunday’s results showed Fillon winning the head-to-head contest against Juppe with 56 percent of support.

With the French left in turmoil, the opinion polls indicate that whoever becomes the center-right challenger is likely to face Le Pen in May’s presidential election runoff.

The polls have suggested Le Pen has only a remote chance of winning that runoff but the more centrist Juppe, 71, had been seen as the best placed candidate to defeat her in a two-horse race.

TARGETS FOR NATIONAL FRONT

A BVA poll in September showed Fillon, who drives racing cars for a hobby, would beat Le Pen by 61 percent to 39 percent if they contest a presidential runoff vote.

But that consensus predates Donald Trump’s U.S. election win, which exposed the same popular anger against political elites as in Western European countries such as France, Italy and Austria that Le Pen has tapped into.

It also raised questions over the accuracy of opinion polls, which were under scrutiny again on Monday in France.

With his socially conservative and pro-business policies, Fillon lacks the broad appeal of the more centrist Juppe, and so may increase Le Pen’s chances of taking power.

Fillon stood down as social affairs minister after big street protests in 2003 when he championed reforms extending the age at which people are entitled to retirement pension payments.

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“We believe Fillon’s lead introduces additional uncertainty when it comes to the presidential election,” said Raphael Brun-Aguerre of JP Morgan in a research note.

But Juppe, who served as prime minister form May 1995 until June 1997 under President Jacques Chirac, would also be vulnerable to National Front barbs.

“Either of the candidates would probably be targeted by far-right National Front leader Marine Le Pen for being part of the old political guard, and Juppe, on this front appears relatively more vulnerable,” said Morgan Stanley in a research note.

Juppe was not giving up.

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“I believe more than ever that the people of France need to come together to turn the page of a disastrous five-year term that has demeaned our country and to block from power the National Front which would lead us into the worst of adventures,” he told supporters on Sunday night.

OPPORTUNITY FOR LEFT?

Fillon and Juppe have clashed most forcefully over Fillon’s proposals to slash the cost of government, notably by axing 500,000 public sector jobs over five years.

Fillon’s plans for market-oriented reforms - including scrapping the 35-hour working week and raising the retirement age - go beyond what his challenger advocates for a country where the state remains a powerful force in the economy.

Born in a western region of France where the secular nation’s catholic roots remain strong, Fillon has said France faces a problem “linked to Islam”. Juppe has sought a more conciliatory tone with France’s large Muslim minority.

Any registered voter can take part in the conservative primaries, and polls showed many of those that did on Sunday were from the left and extreme right.

“The only chance for Juppe is a strong turnout in the second round, including from left-leaning voters. His message will be: we need reforms, but nothing that is horribly painful,” said Claire Demesmay, an expert on Franco-German ties at the German Council on Foreign Relations.

The ruling Socialists and their allies will hold their own primaries in January. President Francois Hollande, whose popularity ratings are abysmal, has yet to declare if he will stand again.

Some on the left hope a Fillon candidacy would provide an opportunity to win back the center ground.

“Ultra-conservative, ultra-liberal, ultra anti-social. Fillon ticks all the boxes,” Jean-Christophe Cambadelis, the Socialist Party’s secretary general, told France Info radio.

Cambadelis appealed to the fragmented field on the left not to split the vote. He urged former economy minister Emmanuel Macron not to run as an independent but instead join the primary contest. Macron swiftly rejected the call, Le Monde reported.

The former investment banker who quit Hollande’s government in the summer launched his outsider run for the presidency last week saying that he was neither of the left or right.

Although a popular politician, polls indicate Macron’s chances of reaching the election’s second round are slim.