The FDJ rider beat his compatriot in a two-man sprint at the end of the 148-kilometre stage around Bois-d'Arcy, posting a time of 3 hours 22min 43sec.

Norway's Alexander Kristoff is nine seconds back in third, while Ireland's Dan Martin and Colombia's Sergio Henao feature among a group of eight competitors that are 19 seconds back.

"The way the race played out changed everything for the finale," Demare told Cycling News.

"Everybody was tired, so I didn’t expect a sprint at the end. 

"Still, it was hard to follow Alaphilippe at the end, but I managed it."

Two-time Tour de France champion Alberto Contador is 1:04 behind in 20th place after falling behind along with Australia's Richie Porte and France's Romain Bardet when crosswinds divided the peloton.

Porte, the champion in 2013 and 2015, is 47 seconds back, while Bardet was excluded from the race for drafting behind a team car.

Race officials disapproved of the way which Bardet joined back onto the chasing group after recovering from a crash with 25 kilometres remaining.

Not long after the stage, the jury announced that last year's Tour de France runner-up had been disqualified.

Tomorrow's 195km second stage will run from Rochefort-en-Yvelines to Amilly.

Paris-Nice is an International Cycling Union (UCI) World Tour event.