Even close allies appeared to caution the inexperienced 39-year-old against complacency ahead of the second round run-off on May 7 against far-right leader Marine Le Pen.
"We need to be humble. The election hasn't been won and we need to bring people together to win," Richard Ferrand, secretary general of Macron's "En Marche" ("On the Move") movement, told BFM television on Monday.
After results emerged on Sunday evening, Macron addressed thousands of euphoric supporters at an election party in southern Paris and brought his wife Brigitte on stage to share in the applause.
"In one year, we've changed the face of French political life," he said to shouts of "Macron! President!"
Later in the evening, he was filmed visiting supporters at the famed La Rotonde bistro in southern Paris, a "Belle Epoque" hang-out for Picasso and other artists where a steak and chips costs 28 euros ($30).
"Macron made a speech as if he'd already won," Le Pen's top aide Florian Philippot said Monday, before attacking Macron for copying the style of former right-wing leader Nicolas Sarkozy.
Sarkozy, who would come to be known as the "bling-bling president", held an infamous victory party in 2007 in a restaurant on the Champs Elysees called Le Fouquet's which was packed with celebrities and business leaders.
He said La Rotonde, one of Macron's favourite eateries, "isn't exactly Le Fouquet's."
Le Pen's National Front (FN) will seek to highlight the centrist's past as a millionaire investment banker, advisor to unpopular President Francois Hollande and pro-globalisation economy minister in the weeks ahead.
"While all Macron's supporters recover from their showbiz evening at La Rotonde, Marine is at a market in Rouvroy," leading FN figure David Rachline tweeted on Monday, showing the far-right leader in a small town in northern France.
Polls published on Sunday night showed Macron comfortably beating Le Pen in the run-off if the vote were held now.
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