In his yellow jersey for a 13th day, the world No 1 looked relaxed after the run from the Camargue into the town of Gap, surrounded by the daunting mountain peaks which lie in wait for the peloton.
"It was a peaceful day, it did me good, we reserved energy in this dreadful heat," said Alaphilippe after a stage raced in temperatures of up to 40 degrees in some parts.
"I'm ready for the Alps," added the 27-year-old former soldier.
"But I need to detach myself from all this going on around me.
"My legs are tired, but in my mind I have never felt better."
Alaphilippe also highlighted his role as leader by intervening in a physical spat between Ineos rider Luke Rowe and Jumbo-Visma's Tony Martin, who visibly rode into the Welshman at the start of a climb.
"Everyone wanted to be in the right position," said Alaphilippe.
"But there were a couple of guys getting nervous, physical about it.
"They thought I might attack I guess so I went over and told them to calm it," said Alaphilippe.
Rowe and Martin were both later thrown off the race as it emerged there had been a little more than simple jostling.
Rowe's Ineos boss Dave Brailsford used a football metaphor to describe the double expulsion as harsh.
"It maybe merited a yellow, but not a red card," said Brailsford.
Rowe had served as a minder to Ineos captain Thomas and told AFP last week he was responsible for getting his man into the right position or his own neck was on the line.
"When the shit hits the fan, he's my responsibility, I believe he will win the Tour, and it's up to me to deliver him to where he needs to be."
Rivals have been predicting local hero Alaphilippe would crack under pressure since he took the overall lead but Thomas' co-captain, Egan Bernal, lying in fifth overall, was unsure.
"We all said he'd lose the lead in the Pyrenees, but here we are with just three stages remaining and he's still there," said the Colombian.
"Hats off to him, he's the one in the lead and he looks strong. But at last we are in the Alps," said impressive climber Bernal, the youngest man in the race.
The victory for Trentin, 29, came after he surged forward alone from a mass breakaway 20 minutes ahead of the main pack, and is a fourth win on the 2019 Tour for the Mitchelton-Scott team after Simon Yates' double and Daryl Impey's victory.
"It's never easy, I was sitting there studying everyone, when it kicked off I just stayed calm in the attacks and I made the move at the right time just ahead of the climb, which won the race," said Trentin, who now has three stage wins on the Tour de France.
"All wins are nice, but I have been chasing this one for a while," he added.
The heatwave was a worry at the first century Roman aquaduct of Pont du Gard where the stage started, with hundreds of fans seeking refuge from the searing conditions by splashing around in the Gardon river.
But Trentin, Olympic champion Greg van Avermaet and six other previous Tour stage winners led a group of 33 riders in a burning pace covering the first 100km in two hours.
"Sure it was warm," said Trentin.
"But we were wearing ice packs and drinking a great deal of water, and when the rain came it cooled us down," he added.