Frenchman Julian Alaphilippe dusted himself off from a fall to claim the first yellow jersey of the Tour de France on Saturday, winning Stage 1 by a clear margin on a crash-marred opening day.

The peloton embarked on the 2021 Tour from the industrial shipyards of this fortified naval stronghold at the western tip of the country to the sound of bagpipes, with hordes of unmasked fans decked out in red-and-white polka dot caps to accompany the black-and-white flag of this fiercely independent region.

World champion Alaphilippe was a pre-race favorite due to the final climb and he shot up the ascent to take 10 bonus seconds at the finish line and also end another 12 seconds ahead of his nearest challenger.

"I was in a great position at the bottom of the last hill, and I accelerated to drop all the sprinters who wanted to win, and then see who was left," Alaphilippe explained.

"We had been planning it and I've been thinking about it since we got to Brittany."

Australia's Michael Matthews is second at 12 seconds while Slovenia's Primoz Roglic came third and is 14 seconds down on the leader in the overall standings.

Crossing the line in his world champion's rainbow jersey, Alaphilippe put his thumb in his mouth in honor of his newborn son with his partner Marion Rousse, a former professional cyclist and now commentator.

Ineos Grenadiers leader Geraint Thomas and defending champion Tadej Pogacar were just behind the winning group on a hugely stressful finish with potential time gaps at stake that almost certainly led to the second of two mass falls on the day.

Thomas and Pogacar emerged unscathed and are just 18 seconds down in the overall standings but both had teammates caught up in crashes.