He averaged 55.45 kilometers an hour — about 34.5 mph — for a stage-winning time of 14 minutes and 56 seconds over a 13.8-kilometer course.
It was the fastest individual stage ever ridden in the history of the century-old race.
Dennis blitzed around downtown Utrecht, the Netherlands, host of the Tour’s “Grand Depart.”
Dennis beat the 21-year-old mark set by Britain’s Chris Boardman over a course that was just over half the length, AFP reported.
“It was nerve-racking watching the screen,” Dennis said. “I didn’t except to go that fast time-wise. When I get to back to the bus, I was told that it was the quickest time trial by my friend back in Adelaide. So that was a nice little bonus, you could say.
“It is possible to win and I’m not just a second-place rider. On my day I’m the best in the world,” he said via AFP.
With that winning ride he also donned the first leader’s yellow jersey of the race.
“It worked out perfectly. Tour de France … yellow jersey … it’s a dream. I have always wished to be in this position and now I am.
“I left it all out there. I went off harder than what I thought I should have and I came back harder than what I thought I could,” he said.
Dennis, 25, rides for the US-based BMC Racing Team.
His teammate, Tejay van Garderen, the No. 1 American rider in the race who’s hoping for a podium spot himself, tweeted congratulations:
Dennis is the seventh rider from Australia to lead the Tour, the world’s premier bicycle race, which runs July 4-26.