Just 11 months after turning professional, Calmejane felt emboldened to face the nine remaining kilometres of the 4.8 per cent average gradient Vixa de Hebeira climb alone, freeing himself from his 19 breakaway companions.
15 seconds after Calmejane crossed the line with his arms in the air, Darwin Atapuma (BMC) out sprinted Ben King (Cannondale-Drapac) for second place and moved into the red leader's jersey.
The other remaining riders of the day's escape crossed the line sporadically including Australia's Nathan Haas who finished fifth and just 23 seconds behind Lilian Calmejane.
Despite his 23 years, the Direct Energie rider said he felt confident he could win the stage.
"I think it possible to win the race at mid race when the gap was four minutes," Calmejan said with a big grin.
"And then I saw Thomas de Gendt very strong in the group and I attacked. When I (was) only (the) first (rider) in the race I give everything to the finish line and it's wonderful."
Atapuma's red jersey follows his victory on stage 5 season of the Tour de Suisse and his near-win at the Giro d'Italia on stage 2 where he led the race until Rein Taaramae (Katusha) cruelly gapped him in the closing kilometres.
Darwin Atapuma took the red leader's jersey (Getty) Source: Getty Images
"This morning I was thinking to go in the breakaway and it was also the plan from the sports directors. There were a lot of breakaway attempts in the first 50km of racing but the peloton wasn't letting them get away.
"I managed to jump in the right one that the peloton allowed to go clear. We had a good advantage in the end with a strong group of 21 riders."
"In the last 5km I knew the GC group was riding really fast so I didn't know if I could get the jersey, so then I attacked to try and win the stage. In the end I was second on the stage but I took the red jersey which is a dream."
A touching gesture
As he crossed the line, Calmejane formed his hands in tribute to former Vendee team mate Romain Guyot who lost his life in March this year after a training crash.
Lilian Calmejane pays tribute to fallen former Vemdee teammate Romain Guyot (Getty) Source: Getty Images
As it happened
Overnight leader Ruben Fernandez (Movistar) and 18 other riders pulled clear from the pack on the stage's first climb. This prompted a concerted and successful effort from Sky to shut down the gap.
Not one to break with tradition, grand tour polka-dot jersey point chaser Thomas de Gendt (Lotto Soudal) crested the category three Alto de Capella first. But he was soon joined by 19 riders who made the break of the day after 40 kilometres raced including Atapuma, Haas, King and Calmejane. De Gendt also grabbed the next lot of KOM points on Alto Monte Caxado but it was only enough to grab the most combative prize and not the polka-dot jersey from yesterday's stage winner Geniez.
With 30 kilometres to go, the break led by five minute advantage and it was clear the peloton happily allowed it to roam. The main favourites appeared to call a truce with only Fernandez trailing off the back of their group as the final climb went upwards.
