Gerardmer, France: Blel Kadri earned France its first Tour de France win this year on stage eight, a 161-km trek from Tomblaine, as race leader Vincenzo Nibali showed a first glimpse of weakness on Saturday.
Nibali retained the yellow jersey by finishing third, three seconds behind Spaniard Alberto Contador.
Twice Tour winner Contador attacked several times on the last ascent and the Italian could not respond to the last acceleration after team mate Jakob Fuglsang was dropped in the final climb.
"Alberto Contador took the race in hand. The last climb suited him more than me," said Nibali.
"It was very difficult and explosive. We've all paid for the efforts of the previous days."
Yvon Madiot, sports director of the FDJ.fr team, agreed the first week of racing had been extremely demanding.
"The Tour will be long for many good riders. I saw a lot of good riders very tired," said Madiot.
American Andrew Talansky, who crashed on Friday, hit the tarmac again on the slippery descent from the Col de la Grosse Pierre with less than 10-km to go.
The Garmin-Sharp rider lost more than two minutes to Nibali and Contador, dropping to 16th overall.
Australian Richie Porte, promoted to Team Sky leader after defending champion Chris Froome pulled out injured following a crash, finished fourth in the stage ahead of French hope Thibaut Pinot.
"I think it is going to be a duel between Nibali and Contador. I'm still a bit behind," said FDJ.fr rider Pinot.
Porte is third overall, one minute 58 seconds behind Nibali, with Dane Fuglsang in second spot 1:44 off the pace.
Contador is sixth, 2:34 adrift of Nibali, just behind fellow Spaniard Alejandro Valverde.
Nibali said the race would not just be a battle between him and Contador.
"The race is not a duel, it's more than that. Richie Porte is up there. He's not here by coincidence," the Italian champion said.
"I've also seen Valverde riding with ease. There have been great riders in action today."
Among them was Kadri who was part of a five-man breakaway.
He attacked in the first climb of the day, 25-km from the finish, and never looked back as he took the polka dot jersey as the leader in the mountain classification.
"Our goal as a team was to win a stage. The polka dot jersey is the icing on the cake," said the AG2R-La Mondiale rider.
Sunday's ninth stage should be quieter for the top guns, a 170-km run from Gerardmer to Mulhouse that is likely to see the breakaway specialists in action.