Deceuninck-Quickstep lead in the foot of the climb, Alaphilippe launched his attack with 2.2 kilometres remaining, riders did try to follow, with Tadej Pogačar and Primož Roglič also jumping clear in pursuit on the steepest sections.
Pierre LaTour (Cofidis) was the closest to being able to follow the reigning world champion, but along with Roglič and Pogačar, he was reabsorbed into the chasing group before the finish. The group regained some ground on Alaphilippe but it wasn't enough to prevent the French star from winning in style.
"It’s really incredible, honestly," said Alaphilippe. "It’s a scenario I imagined and the start of my Tour is a success. It’s a super feeling, my team did great work, they took care of me and controlled things.
"In the final, I was caught up in a crash but I was able to stay calm and then I had to finish off the work on the final climb, where we really wanted to make it hard and get rid of the sprinters. When Dries (Devenyns) opened the gap I gave the maximum without asking any questions.
"It wasn’t planned to go from that far but when I went I saw I had a small gap and I saw everyone was à bloc so I decided to keep going. In the final kilometre, I saw the gap wasn’t coming down. Every time it’s an emotion I can’t describe.”
Australian Michael Matthews led the sprint from behind to take second on the day, with Roglič a close third on a day where a number of pre-race favourites saw their bids for overall glory at the Tour de France take a significant hit after being caught up in the crashes that cast a shadow on the stage.
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Five riders managed to go clear at km 12 at the initiative of Franck Bonnamour (B&B), quickly rejoined by Danny van Poppel (Intermarché-Wanty Gobert), Cristian Rodriguez (TotalEnergies), Anthony Perez (Cofidis), Ide Schelling (Bora-Hansgrohe) and later by Conor Swift (Arkea-Samsic) to make a front group of six after 20 kilometres of racing. Eight kilometres further, their maximum advantage was 3’55’ and the break was set for the day.
After some skirmishes on the climbs for the honour of wearing the first mountains jersey of the race, Ide Schelling escaped the early break with a big attack. He immediately built up a gap and the rest of the escapees faded back to the peloton.
It was a stage marred by massive crashes within the main bunch from then on. First, a large crash was caused by a spectator encroaching onto the course with 46 kilometres to go, felling Tony Martin who in turn crashed into the middle of the peloton, bringing down a large number of riders and the crashed riders filled the road.
Some were slow to pick themselves up with Jasha Sutterlin (Team DSM) abandoning the race soon after. The race continued after a lull within the main bunch to allow the fallen riders time to rejoin. After that, the pace was picked up again, capturing the lone remnant of the breakaway, Schelling, before the final 20 kilometres run to the line.
There was another crash with 7 kilometres to go, this time at higher speed, with again a large number of riders hitting the road hard. Chris Froome (Israel Start-Up Nation) appeared the worst injured but managed to remount and nurse his way into the finish.
As riders, team staff and medical first aid swarmed at the crash site, there was still a race to be won, and Deceuninck-Quickstep moved to the front of the race to make sure they arrived first at the foot of the final climb of the Côte de la Fosse aux Loups.
With the hardest section of the climb coming within the first kilometre and a half of ascending, the first attack proved to be the decisive one as Alaphilippe surged away from his rivals. While riders made desperate attempts to bridge over to the world champion, it became evident that the chase was in vain, with Alaphilippe posting up to celebrate the win.
The Tour de France continues with Stage 2 a 183.5 kilometre stage from Perros-Guirec to the steep finish atop Mur-de-Bretagne. Watch the action on SBS from 2030 AEST, with live racing starting from 2100.