Porte, who lost 51 seconds in the opening stage after being delayed behind a pile-up, helped his team edge out Team Sky by four seconds after they completed the 35.5 kilometre circuit around Cholet in 38 minutes 46 seconds.
"The only thing I can really understand from it was that Chris didn't even go to the adverse analytical finding, it didn't even get to that stage, he was asked to explain himself which he got given due process to do and he was cleared by the people that run the sport and doping agency and that's all we really know. We're on track but there's still so much to go through".
He told ITV4: "We did an awesome job, the boys were unbelievable and previous year at the team time trial at the Worlds no one suited up as the strongest and there was not much difference between everyone again today and that's exactly what you want".
Van Avermaet's teammate Tejay van Garderen finished on the same time to take second place overall with Sky's Geraint Thomas in third.
Overall, Froome is in 18th place, 55 seconds off the pace and still 44 behind 2017 Giro d'Italia victor Dutchman Tom Dumoulin, who with Team Sunweb only lost seven seconds to the Briton today.
"It's about what I expected, we thought we'd lose a bit to Froome and we lost a bit to Froome", said the dry-witted Quintana.
"I was counting down the hours until it began and the first day is one of the best of the year". "That's the nature of the game".
"Revenge? I already forgot about previous year", Sagan said. They were only seven seconds back and on a similar trajectory to us so you do have to wait.
Tom Dumoulin was about the only general classification rival not to concede significant time to BMC and Sky, with his Team Sunweb team finishing fifth, 11 seconds down.
His acceleration away from his rivals showed there is no reason why Gaviria should be intimidated by Sagan et al, and the fact that he had time to sit up and celebrate when crossing the line showed how comfortable his victory was.
Among the big losers today were Nairo Quintana, whose Movistar team came home 53 seconds down on BMC Racing, Bahrain-Merida with 2014 Tour de France victor Vincenzo Nibali, 1 minute and 6 seconds down, and Romain Bardet's AG2R-La Mondiale, who came home 1 minute 15 seconds behind the day's victor. Martin and his team-mates lost 2-28 minutes to Team Sky and slightly less to the other top teams and riders.
Froome, who fell heavily before the Giro d'Italia prologue but rallied two weeks later to two spectacular stage wins that won him the Tour, added: "There's still a great deal of road on the way to Paris".
Had the team not lost so much in the team time trial, he perhaps could have won the race overall. We just wanted to get that stage. "We were close but not quite quick enough".
Britain's Mark Cavendish, who has 30 stage wins, said it was the hardest Tour de France route he'd ever seen and doubted he'd make it to the mountains. In the last week, they have been drilling their team time trial as well as riding the cobbles of the Roubaix stage nine.
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