"Unbelievable, unbelievable", the 21-year-old Pogacar said after Roglic laboured to the finish, no longer in the race lead.
All the more so as Roglic has previously produced outstanding time-trial performances at the 2019 Giro d'Italia through the Tuscany vineyards and later that year on his way to Vuelta victory on the stage 10 time-trial at Pau.
Staggeringly, the youngster will also pull on the polka dot jersey as best climber on the Tour, and also the white one as best under-25s rider.
Roglic, who had worn the yellow jersey for 11 days, sat on the ground grieving after blowing his lead but got up to hug and congratulate his countryman - Slovenia's first Tour champion.
"When I'm asked if Primož will win, I tell them he's already our victor", said Matjaz Svagan, mayor of Roglic's hometown, which has readied billboards that read "Primož Roglic our pride". The team has done an fantastic job, I have the (yellow) jersey but we have all worked for it.
"I'm really proud of the team". I knew every corner on the road, thanks to the work of my team.
The upset echoes that of the last day of the 1989 Tour de France when American Greg LeMond won the race by eight seconds over France's Laurent Fignon after starting the time-trial 50 seconds off the pace.
"Chapeau to Tadej, he obviously deserved it", the 30-year-old said.
"I have taken my body to the limit but there came a point where it told me enough and as a defence mechanism has blocked me".
"When I saw that Carapaz was dropping the speed, I thought now it's the time to go and went all in to the end", Kaemna said.
"I can still be happy with the result and the racing we showed so let's take the positive things out". Just moments after they'd run out of breath on a short hill climb in pursuit of Italian rider Matteo Trentin, third in the green jersey standings, Andersen pounced.
Australian Richie Porte will complete the podium, having ridden his way from fourth to third overall in the time trial to the Planches des Belles Filles ski station in eastern France.
"Unbelievable, unbelievable", Pogacar said.
"Tomorrow it's all on me".
Britain's Adam Yates of Michelton-Scott will finish ninth in the general classification, 9mins 25secs behind the victor.
Though not quite there mathematically, Bennett looks all but certain to win the classification barring an incident between now and Paris on Sunday.
Sunday's finish into on the Champs-Elysees is traditionally contested by sprinters from each team, with Ireland's Sam Bennett holding a big lead in the battle for the green points jersey over seven-time victor Peter Sagan of Slovakia.
It's going to be a dream arriving into the Champs Elysses wearing the green jersey, it's going to be an fantastic experience. This always gives you some extra energy, it is such a unique feeling.