Welshman Thomas wins 14km time trial in 16 minutes and four seconds.
Froome sixth as Team Sky teammate Thomas wins Stage 1 of Tour de France
Geraint Thomas won his first career Tour de France stage and took the yellow jersey as Team Sky enjoyed a dream start to the 2017 edition on the soaking streets of Dusseldorf.
Welshman Thomas completed the opening 14-kilometre time trial in 16 minutes and four seconds to win by five seconds from BMC Racing's Stefan Kung.
His teammate Chris Froome finished sixth, 12 seconds down, as he opens his bid to win a third straight Tour crown and fourth overall.
Thomas was forced to withdraw from the Giro d'Italia in May after he suffered a shoulder injury during the ninth stage, but he put that behind him with the victory in Germany.
"It's unreal. The start of my eighth Tour, my 12th Grand Tour and my first stage win. It's been a long time coming and it's just an amazing feeling. I didn't even dream about it last night," the Welsh rider told ITV4.
"It's been a rough time on the bike this year and it's nice to finally... it certainly makes up for most of the Giro, and back home as well. With my mum and my wife I've had a bit of a rough time recently so it's nice to get this win.
"It's unbelievable. I'm lost for words.
"I've got a tendency to go about a bit hard but I'm getting older now and I'm learning my lessons, and today couldn't have gone any better."
Froome was comfortably the best of the general classification hopefuls as Sky made a major statement in the treacherous conditions.
BMC's Richie Porte, seen as Froome's main rival, crossed in a time of 16 minutes 51 seconds, while there was worse news for Nairo Quintana and Movistar as key man Alejandro Valverde crashed out of the race.
For all the pre-race talk of a weakened Team Sky, they finished with four riders in the top eight as Vasil Kiriyenka was third, seven seconds back, and Michal Kwaitkowski eighth, 15 seconds down on Thomas.
"It's really great for the team that Geraint has won," Froome said. "The time trial is something I've worked on during the past three weeks and we've taken time on rivals too, which is a great start."
Germany's world time trial champion Tony Martin of Katusha-Alpecin had been favourite to take the stage on home turf but had to settle for fourth place, eight seconds off Thomas's time.
The victory will be extra sweet for Thomas, who was given the chance to lead Sky in the first grand tour of the year but saw his dream of winning the Giro ended by a freak crash caused by a police motorbike at the end of the first week.
* Press Association