Mathis finished the 28.9km course 18 seconds ahead of his compatriot Maximilian Schachmann and 37 seconds ahead of Australia’s Miles Scotson.
He was the second rider to start and finished in a time of 34min and eight seconds. He then waited until the last starter, 2015 defending champion Mads Wurtz Schmidt of Denmark, completed the course. The Dane faded badly to 21st and Mathis could start to celebrate.
“It was so long in the hot seat,” Mathis said. “But it was my kind of course, absolutely flat and technical. Really, I have no words to express how well it went, and how pleased I am.”
Scotson, the 2015 under 23 national time trial champion, was the 25th of 74 riders to start and held a consistent pace throughout the race tp stop the clock in 34 minutes and 46.07 seconds.
"There's always things you would do differently," Scotson said. "I probably rode at the highest temperature of the day but so did the guy who got silver.
"He obviously did an exceptional job. He said he thought he went out too hard, and I was the same.
"Temperatures like this, 37 degrees, in Australia, it wouldn’t bother you that much over the summer.
"We’ve done some heat adaptation work, but it surprised me the way my body responded in that heat. I thought I would cope with it better in 37 degrees than I did today but it must be a different kind of heat here."
Scotson's younger brother Callum, placed 10th overall, 1min 22sec down on the winner.
The junior women's event was won by Karlijn Swinkels of the Netherlands ahead of Lisa Morzenti (ITA) by eight seconds and 22 seconds ahead of Juliette Labous of France.
“I came here on Thursday, we did a recovery ride on Friday and then on the second day, I rode on the course and I did every curve ten times to make sure it was perfect,” Swinkels said.
Australia's Madeleine Fasnacht (TAS) finished ninth while Chloe Moran (SA) completed the course in 15th place.