Fillon, a former prime minister who wants to raise the retirement age, cut back social security and scrap the 35-hour working week, would easily beat National Front leader Marine Le Pen in a run-off second round, a flash opinion poll said right after his primaries victory.
But to do that, the 62-year old former prime minister and admirer of late British prime minister Margaret Thatcher now faces the challenge of bringing voters behind a program that promises radical change.
"I must now convince the whole country our project is the only one that can lift us up, for jobs, growth and to fight those fanatics that declared war on us," a visibly moved Fillon said at his campaign headquarters.
"I will take up an unusual challenge for France: tell the truth and completely change its software," said Fillon, a racing car enthusiast who lives in a Loire valley chateau.
With votes from nearly all of 10,229 polling stations counted, Fillon had won 66.5% of the votes in the primaries organized by the center-right Les Republicains party.
Next year's presidentials in the euro zone's second-largest economy are shaping up to be another test of the strength of anti-establishment parties in Western countries, with French voters angry with stubbornly high unemployment and fearful after a wave of Islamist militant Attacks.
