To arrive to the top with a time of 14-56 minutes over 13.8 kilometres, he beat Fabian Cancellara (Trek Factory Racing) and Tony Martin (Etixx-Quick Step), home favourite Tom Dumoulin (Giant-Alpecin), and former Hour Record holders Alex Dowsett (Movistar) and Matthias Brändle (IAM Cycling).
The 25-year-old Australian hugged his girlfriend and warmed down under the red and black awning of the BMC bus. He looked at his time, those to come after him, and said that it was still a long way to go for him to take such a famed jersey.
He explained, "I went out harder than what I thought I should've and came home harder that what I thought I could've."
The attention, which was vaguely there at the bus, multiplied astronomically under the Tour podium on the hot seat. Mr Dennis slowly, one rider after another, became Mr Utrecht as the locals celebrated the Tour de France's first visit to their city.
"It's definitely the high of my career," Dennis said.
"It sunk in five minutes to go when I saw most of the biggest threats coming in behind me. It was almost surreal."
His time over the 13.8-kilometre course gave him the fastest ever average in a Tour time trial at 55.446 kilometres an hour. It was untouchable by the time trial greats like Cancellara and Martin.
Sky's Chris Froome and others noted that the wind around the cycling-mad Dutch city kicked up in the afternoon. Dennis could have saved himself a few seconds by deciding to start early, the 38th of 198 cyclists to begin the 2015 Tour.
The wind has blown in favour of Dennis for much of 2015. He took on and beat Richie Porte (Sky) to win the Tour Down Under. He drew Bradley Wiggins's attention with his Hour Record ride. As soon as Wiggins finished the first stage of the Tour of Qatar, he asked about the young Australian's Hour Record distance.
Dennis covered 52.491 kilometres in February, a mark that stood up until Dowsett and Wiggins came along with the summer months of May and June. The stage and yellow jersey to open up the Tour de France only continued a stand-out season.
"It's a little bit of a shock," added Dennis. "I've been working a lot with the team. I came early, about a month earlier, just to check out the course and recon.
"At the Tour, to get the yellow jersey, it's a dream. I always wished to be in this position, now I am."
Dennis explained that hopes that he can keep the jersey for at least one day and that he wants to keep the pressure off his team-mate and overall contender, Tejay van Garderen.
Tomorrow, the Tour cyclists face a flat and windy day along the coast and on Monday, a stage that ends up the famous Mur de Huy in Belgium. On Tuesday, the race enters its French homeland with a cobbled stage to Cambrai. Dennis will have his work cut out for him, but he has already proven this year to be a capable winner.
Video: Secrets of the toolbox - BMC
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