Strong winds and wet conditions disrupted a stage that was expected to be one for the sprinters.
And a sharp climb inside two kilometers of the finish put paid to the challenges of highly-fancied pair Marcel Kittel and Andre Greipel, who both blew up on the incline and missed out on the sprint finish.
A break by Arnaud Demare and Julian Alaphilippe sent the pair clear going into the home straight and Demare – the superior sprinter of the two – survived a kick from his compatriot and managed to avoid getting boxed in against the railings to power through and take the stage.
Twice Tour de France champion Alberto Contador was trapped behind with Australian Richie Porte and France’s Romain Bardet when crosswinds split the peloton and he lost further ground in the finale.
Contador (Trek Segafredo) lies 21st overall, 1:14 behind Demare.
Among the favourites for the overall title, Ireland’s Dan Martin (Quick Step Floors) and Colombian Sergio Henao (Team Sky) are 19 seconds off the pace.
Porte (BMC), winner in 2013 and 2015, lies 57 seconds behind Demare, as does Bardet (AG2r-La Mondiale) after the Frenchman, who finished second overall in last year’s Tour de France, recovered from a crash 23 kilometres from the line.
“Apparently it’s nothing serious,” Bardet’s team manager Vincent Lavenu said.
The 195km second stage on Monday will run from Rochefort-en-Yvelines to Amilly.