Froome slipped behind after suffering a suspected broken spoke as Romain Bardet's Ag2r La Mondiale team ramped up the pace. Frome stopped, swapped his rear wheel with Michal Kwiatkowski and chased for around eight kilometres.
"It couldn't' have come at a worst time today," Froome said. "Certainly the speed was probably at the highest point of the race, coming in to the foot of that last climb. It was really a bad moment.
"I'm grateful Kwiatkowski stopped, and all my team-mates paced me, even Mikel Landa dropped back and paced me. If I didn't get back, I wouldn't expect to be in yellow this evening. I had to get back, or it was game over for me."
He stopped to change the wheel on the approach to the penultimate climb of the day, and by the time he had remounted the time gap from him to rivals Bardet and Fabio Aru (Astana) had shot up to 50 seconds.
Mikel Nieve and Sebastian Henao went to work to bring him within touching distance of the group of GC contenders. Eventually, Mikel Landa dropped back to pace Froome over the last gap, rejoining at 32.7km to go.
Watch: Tour de France stage 15 highlights
Froome said he thinks he “broke a spoke”, saying “the wheel wasn't straight.” He was gesturing to his team-mate shortly before he stopped.
"That was extremely stressful, panic station. I really thought that could be the yellow jersey changing hands again. I'm very grateful for my team-mates doing the work to help me," added Froome
"It was almost as if I had to attack just to get back to the front group, I had to go very deep. I had to, I had no option. It was either that or not going over the climb with the favourites."
Some questioned Ag2r's aggressiveness with the yellow jersey stopped due to a mechanical issue. The same issue arose with Fabio Aru’s attack on the stage to Chambéry a week ago.
"When the pace went up, that's when I had the issue," continued Froome. "I can't blame them, they rode a great race today and caught some of the GC guys out. Chapeau"
Nairo Quintana (Movistar) slipped behind by nearly four minutes today. Ireland's Dan Martin (Quick-Step) attacked in the final and gained 14 seconds, jumping ahead of Landa to fifth overall.
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