1239 GMT February 24, 2020
Fillon, a former prime minister who vowed to change France's "software" with an assault on public sector spending, moved one step closer to the Elysee by securing a resounding victory over Alain Juppe in the Les Republicans primary vote on Sunday.
The ruling Socialists, meanwhile, sought to quell talk of a fallout between deeply unpopular President Francois Hollande and his prime minister, Manuel Valls, over which of them should seek the party ticket in their primary set for January, Reuters reported on Monday.
Opinion polls show, though, that whoever does run for the Left is likely to be a very distant third behind Fillon and the National Front (FN) leader Le Pen in the election's first round next April.
Fillon, 62, easily saw off Juppe, another former prime minister, by securing two-thirds of the vote on Sunday.
"When a candidate wins with a score of that size – two-thirds – it creates a natural momentum, a center of gravity and a unifying force," Bruno Ratailleau, a Fillon ally and senator from western France, told RTL radio.
Ex-president Nicolas Sarkozy, whom he ousted in the first round of the conservatives primary, and Juppe had both been given far better odds of winning the ticket at the start.
Both men rallied behind the 62-year-old Fillon after his triumph.
But Fillon's hard-line reforms plans – cutting public spending by 100 billion euros over five years, scrapping a tax on the wealthy and pushing the retirement age to 65 and cutting public sector jobs – hand a glimmer of opportunity to Hollande and his Socialists, and the broader French Left.
His plans also set him apart from the anti-euro, anti-immigration Le Pen's more pro-worker policies.
Fillon's social and economic policies could also push more centrist voters toward the left – if there was a rallying candidate.
Fillon, an admirer of late British prime minister Margaret Thatcher, pledged on Sunday to introduce radical change.
"I will take up an unusual challenge for France: Tell the truth and completely change its software," Fillon, a racing car enthusiast who lives in a Loire valley chateau, told supporters.
French voters are angry with unemployment – stubbornly high at 10 percent – and fearful after a wave of Islamist militant attacks.