President Macron left the talking to his prime minister, Gabriel Attal, but he did issue a statement, saying the time had come for a “broad, clearly democratic and republican alliance for the second round”.
While other leaders addressed cheering supporters, Mr Attal made a short, solemn address outside his residence at Hôtel Matignon.
“Not a single vote must go to the National Rally,” he declared. “The stakes are clear – to prevent the National Rally from having an absolute majority.”
“One thing is for sure,” said Jean-Luc Mélenchon, the abrasive leader of France Unbowed (LFI), ” Mr Attal won’t be prime minister any longer.”
His is the most radical of the left-wing parties that make up the New Popular Front, which finished within a few points of National Rally.
However, he agreed with the prime minister that not one more vote should got to RN.
It has been a long journey for the National Rally, from its roots on the extreme-right fringe of French society to securing the support of one in three French voters.
They have a charismatic young leader who could be France’s next prime minister, and a set of policies that range from banning mobile phones in classrooms and cutting taxes on energy to removing benefits from foreigners.
“People aren’t happy when there’s insecurity on the streets,” a voter called Patrick said in one of RN’s potential new strongholds east of Paris.
“Victory is in sight,” said Eric Ciotti, a conservative leader who split his Republican party and formed an alliance with National Rally that he called “unprecedented and historic”.
France has entered uncharted territory, says commentator Pierre Haski, and there are only bad outcomes. “That’s why a lot of people are angry with President Macron,” he told the BBC.
RN has a chance of an absolute majority, although the more likely outcome at this point may be a hung parliament with RN holding the biggest number of seats. The New Popular Front could also increase its share of the vote, buoyed by voters from other parties.
Next Sunday’s run-off round will feature either duels between two parties, or three-way races. There were only a handful in the last election, but the high turnout means that more than 300 third-placed candidates qualified for these “triangular” battles.
What will now be decided, largely on a local constituency level, is whether the third-placed candidate will drop out of the race to stop RN from winning the seat.
Prime Minister Attal said that in “several hundred” constituencies, his party’s candidates would be best placed to block the RN.
It was a moral duty to bar the far right from “governing the country with its disastrous project”, he said.
But many centrist candidates who came third are expected to step aside, if a Socialist, Greens or Communist rival has a better chance of beating RN.
On the whole they may refuse to give way to Mr Mélenchon’s party, although one Macron candidate who qualified in third place said she was standing down to allow LFI rival Francois Ruffin a better chance of victory.
“I draw a line between political rivals and enemies of the republic,” Albane Branlant said.
Jean-Luc Mélenchon said where his party’s candidates were in third place and RN was in the lead, they too would withdraw.
In the words of Mr Macron’s Socialist predecessor and former boss, François Hollande: “We have an imperative duty to ensure that the far right cannot win a majority in the Assembly.”