Millions of French voters were casting ballots Sunday to pick the presidential candidate for the centre-right Republicans party, with ex-premier Francois Fillon tipped to win and become favourite for next year's election.
The US-style primary contest, the first for the party, is a battle between socially conservative and economic "radical" Mr Fillon and the more moderate Alain Juppe, also a former prime minister who is nine years older at 71.
The French presidential vote is seen as a key test for mainstream political parties after the success of Donald Trump in the United States and the Brexit campaign in Britain, both of which harnessed anti-elite, anti-establishment anger.
Polls opened at 8:00 am (0700 GMT), with all French voters who pay two euros (£1.70) and state they share the values of the centre-right allowed to cast a ballot.
Whoever wins will face fierce competition from far-right National Front leader Marine Le Pen, who is waiting in the wings ready to attack the victor as a symbol of France's ruling class.
Mr Fillon, a career politician and prime minister from 2007-12, has warned that France is "on the verge of revolt" and believes his plan to slash 500,000 public sector jobs and business regulations is the tonic the demoralised country needs.
"I'll do everything for entrepreneurs!" he declared at his final rally on Friday night in Paris, promising to help businesses create the jobs needed to lower France's stubbornly high unemployment rate of around 10 percent.
The devout Catholic and motor racing fan has also won support with his hard line on Muslim immigrants, as well as an emphasis on protecting France's identity, language and family values.
He demanded Friday that "the Islamic religion accept what all the others have accepted in the past... that radicalism and provocation have no place here."
Mr Juppe, meanwhile, has made a pitch for the centre-ground, accusing his opponent of wanting to reform France with "brutality" with an unrealistic programme that has drawn support from the far-right.
As well as promising to shrink the French state, Juppe's signature announcement was a promise to seek a "happy identity" for multicultural France despite worries about the threat of immigration and Islamic extremism.
"I am best placed with my programme to beat Marine Le Pen," Mr Juppe said on the last day of campaigning on Friday.
He has also sought to highlight Mr Fillon's conservative views on abortion and gay marriage, as well as his closeness to Russian President Vladimir Putin who praised Mr Fillon last week as a "very principled person".
But it is Mr Fillon who has all the momentum heading into Sunday's run-off vote.
He won the first round of the primary last Sunday with 44 percent and has since picked up endorsements from party heavyweights including former President Nicolas Sarkozy, who was knocked out last weekend in perhaps a final blow to his political career.
Several surveys last week forecast Mr Fillon to emerge as winner on Sunday with around 60 percent, but after a topsy-turvy year that has made fools of analysts and pollsters, no one should take his victory for granted.
As well as Ms Le Pen, Sunday's winner will face competition in next year's vote from a Socialist party candidate, probably President Francois Hollande who appears intent on trying to defy his historically low approval ratings.
After a troubled five years in power, a survey on Friday showed current Prime Minister Manuel Valls would be a far more popular candidate than Mr Hollande.
Mr Valls did not exclude making a run at the candidacy in the socialist primary, saying "I will make my decision with a clear conscience", in an interview published by weekly Journal du Dimanche.
Mr Hollande's former protege and economy minister, 38-year-old Emmanuel Macron, is also set to stand for the presidency as a centrist independent, injecting some youth and another element of uncertainty into the race.
Far-left candidate Jean-Luc Melanchon is also likely to draw votes away from mainstream parties in a trend seen in elections across Europe following years of austerity and anger over globalisation and job losses.
Current polls forecast that Ms Le Pen and the Republicans' candidate will make it through to the final run-off round of the election in May, with the latter set to win by drawing moderate voters from the right and left to block the far-right.
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