"It was a fantastic finale, it was lovely to go together like this and we showed that we can work together even if we're in different teams", said Alaphilippe, whose move was highly expected as bonus seconds were up for grabs in the ascent to the Cote de la Jaillere and at the finish.
The long day's simmering tension erupted with 15km to go when Canadian Michael Woods (EF Education First) lost control on a tight right hand corner and took out a batch of Team Ineos riders hot on his wheel.
De Gendt rode away immediately after the 200km stage from Macon kicked off alongside three other riders, and was the last survivor of the leading quartet not to be caught by the peleton.
Alaphilippe reclaimed the overall leader's yellow jersey and Pinot leapfrogged Thomas in the general classification after gaining 28 seconds on the 2018 victor.More news: Teen bomber kills at least five at eastern Afghanistan wedding
Carrying the hopes of a country that has not seen a homegrown Tour victor in 34 years, the French pair emerged as the big winners on the latest stage, which saw Geraint Thomas crash and lose ground in the defence of his title.
"I had a really good feeling all day so I believed in it all day, but we only got five minutes (lead) and it went down really quick to three and a half", De Gendt said. It hurts so much but it's wonderful.
Thomas had his team mate Michal Kwiatkowski to thank for his recovery.
"Gianni hit the deck first with G (Geraint Thomas)". I got tangled in Gianni's bike and took some time to get going. I was trying to catch the group again in case there was another mechanical or a fall.More news: Sudan military stop attempted coup, arrest involved security officers
Uninjured, Thomas remounted and with the help of several teammates, was able to bridge across to the peloton and eventually finish 10th.
"There is pressure obviously but the biggest pressure is the one I put on myself", said Pinot, who abandoned the race in 2016 and 2017 and did not take part a year ago after failing to fully recover from a bout of pneumonia sustained near the end of the Giro d'Italia. "I've had very good feeling already for the whole Tour and I had fantastic legs today". You just don't want to give any unnecessary time away. "It's just frustrating that those two got time". Michael Matthews (Team Sunweb) +0:26 5. I know it's there.
"We made a decision to ride to give me a shot at the stage and I think we did a really good job", he said.
"It is hard, but I love it".More news: Super 30 Day 2 in overseas
There's no let up on Sunday - France's national day - with Stage 9 presenting an equally relentless 170.5km of rolling terrain.
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