The Irishman finished 33rd on the 27.2-kilometre test, losing 2:06 to stage winner Julian Alaphilippe, and 1:56 to race favourite Geraint Thomas. The result sees Martin slip two places on the overall standings, from ninth to 11th, but the time loss is more troubling.
Previously, Martin had lay just 57 seconds down on reigning champion Thomas, with his favoured terrain of the Pyrenees nearing. Now, as the Tourmalet looms, he has 2:49 to make up on the Welshman.
"The heat was the biggest surprise, you know," said Martin after the stage. "This morning by noon, the temperatures had gone up so much, and on the first climb I felt it straight away.
"[The stage] went really quick, you get into your rhythm. It's a cool course and you have to concentrate at all times. I went as hard as I could, and that's all I can ask for."
Martin, a climber who enjoys the steep slopes far more than time trialing, targeted the first half of the TT, the hillier section. Though he actually lost 6.75secs/km to Alaphilippe at the first checkpoint, his times stabilised as the race went on, only losing 3.79secs/km to the stage winner on rest of the course, and riding steadily on the flat.
"A lot of it was about timing, and that was it," he said. "The plan was to go hard at the first part and then hold on to the finish line, but that's what you do.
"You go out and try to get to the finish. I'm improving a lot, and that's thanks to the team. We'll keep working on it. I did my best."
With the time trial – Martin's biggest weak point in grand tour racing – out of the way, he'll be relishing the challenges of the final week. The Pyrenees, scene of his first Tour stage win in Bagnères-de-Bigorre six years ago, and the Alps, are where the fightback begins.