Australian Rohan Dennis (BMC Racing) took confidence in the World Championship time trial from knowing Tom Dumoulin's power numbers.
Dennis powered through the course to hold off the charge from Team Sunweb's Dutchman behind trying to defend his title.
Dumoulin clocked a time 1-21 minutes slower over 52.5 kilometres.
"It's an amazing feeling," Dennis said.
"I've been coached from the car by [team coach] Brad McGee. He kept me calm. Knowing Tom Dumoulin's watts during the team time trial made me confident that I'd beat him but I didn't want to be sure until I'd crossed the line."
Dennis' confidence even had him considering a victory salute, but the former hour record holder did not want to ruin his first shot at a rainbow jersey.
"It's a dream come true to be the world champion. I've been chasing this since I was a junior... I've never won it in any age group. I'll enjoy the next year in the rainbow jersey for sure."
Dennis, who signed for team Bahrain-Merida for this coming 2019 season, wore the pink jersey in May after finishing second to Dumoulin in the Giro's opening time trial and taking time bonuses in the second stage.
Ahead of Tony Martin (Katusha-Alpecin) and Dumoulin, he won the Giro's long time trial.
In the Vuelta a España, he won both time trials.
The opening day gave him the leader's red jersey and the long time trial win in stage 16 gave him a good confidence boost. He abandoned the race that night to prepare specifically for the Worlds.
The Australian team estimated Dumoulin's power based on the team time trial on Sunday. Quick-Step won ahead of Sunweb and BMC.
"I knew the power that we rode in the team time trial. We lost 19 seconds and I held higher power up the hill than I did in the team time trial," Dennis said.
"I knew that Tom rode the front of the team time trial and he was pushing pretty hard so I had a fairly good idea of what power I needed to hold. I think I was 35 seconds in front at the bottom and when I got to the top, I was fairly confident that I had at least done the same time as him."
Dumoulin completed a grand slam of sorts. The second place silver medal matched the runner-up spots he had in the Giro d'Italia and Tour de France.
"I am still second, but I was far away from my top level," Dumoulin told NOS television.
"I was unsuccessful on the bike. I tried to get my power from everywhere except it wasn't in the right way. My whole body cramped.
"I could not get off my bike. I have a block for a head, that's why it worked. I just wanted it so much so I can push myself to great highs.
"I can only win against Dennis, though, if I am in top shape. The top form was not there today."
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