“Extremism can only bring unhappiness and division,” said the defeated candidate of the center-right Républicains party, François Fillon, who was the consensus favorite four months ago but was brought down by a corruption scandal. “There is no choice but to vote against the far right,” said Mr. Fillon, who was set to finish in third place.

The candidate of the governing Socialist Party, Benoît Hamon, whose fifth-place finish symbolized voter rejection of the establishment, was equally unequivocal. He had run a campaign of unrelenting hostility toward Mr. Macron. That vanished Sunday. “There’s a clear distinction to be made between a political adversary and an enemy of the republic,” Mr. Hamon said, calling on Socialists to vote for Mr. Macron. “This is deadly serious now.”

Only the likely fourth-place finisher, the far-left candidate Jean-Luc Mélenchon, was holding back on Sunday night, hoping for an as-yet uncounted big-city vote that might push him past Ms. Le Pen. But his supporters were already acknowledging what appeared to be inevitable and calling for a Macron vote in the second round.