PARIS: Francois Fillon heads into a five-day runoff campaign for France's conservative presidential ticket as favourite over opponent Alain Juppe after a stunning first-round vote result that ousted ex-president Nicolas Sarkozy from the race.

Market analysts say the outcome opens up fresh uncertainty about the result of next year's actual presidential election, potentially increasing a still remote risk that far-right leader Marine Le Pen can win it.

Before that though, Fillon is up against another former prime minister, Alain Juppe in a second round of the primaries on Nov. 27. Juppe has a week to turn around his momentum-sapped campaign and win over the supporters of the other candidates.

With Fillon only six points short of the 50-percent threshold needed in the first round and Sarkozy on his side, it looks a tall order for Juppe.

However, any French voter can take part in the run-off next Sunday, and the views of pollsters and commentators have been much confounded in popular votes worldwide this year - not least Sunday's vote in which Fillon did far better than expected.

At stake is an almost certain place in the second round of next spring's presidential election, pollsters say, with the French left in turmoil under the deeply unpopular President Francois Hollande.

In that decisive poll next May, the conservative challenger would in all likelihood face National Front party leader Marine Le Pen.

A BVA poll in September showed Fillon beating Le Pen by a margin of 61 percent of votes to 39 percent, but recent opinion poll scenarios have not pitted him against her.

With his socially conservative and liberal, pro-business platform, he lacks the broad appeal of the more centrist Juppe, and so arguably increases the perceived risk that Le Pen could take power.

"To some extent, 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.

A snap poll by Opinionway showed Fillon winning next Sunday's head-to-head contest against Juppe with 56 percent of support, but Juppe was not giving up.

"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 his supporters on Sunday night.

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

Behind his still-boyish looks and refined demeanour, the 62-year-old Fillon stands out as a hardliner on government spending and liberal economics.

"BREAK FROM BUREAUCRACY"

His proposals 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, even for the centre-right.

"My fellow Frenchmen have told me, everywhere, they want a to break away from a bureaucratic system which saps their energy," Fillon, an admirer of the late British Prime Minister Margaret Thatcher, told his campaign faithful.

Juppe, who had led the polls for weeks, last week dismissed Fillon's proposal for public sector job cuts as impossible, saying a gentler reduction was needed. Juppe also proposes easing the tax burden on households.

Either way, next year's presidential and legislative elections are shaping up to be another battle of strengths between weakened mainstream parties and rising populist forces.

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

Some commentators were saying on Monday that if Fillon wins the conservative ticket over Juppe, the left could find new impetus as a space opens up for them in the centre.