Nairo Quintana admitted he let his guard down on stage eight of the Tour de France, allowing Chris Froome to take the win and move into the overall lead.

Quintana had matched general classification rival Froome throughout most of the 184-kilometre ride from Pau to Bagneres-de-Luchon, but an error on the final climb saw the Team Sky rider take advantage.

Having seen his attempts nullified earlier on the Col de Peyresourde, Froome pushed one last time near the summit as Quintana tried to cool down and there was nothing the Colombian could do.

Froome descended superbly to take the stage and open up a 23-second lead over his rival, leaving Quintana ruing a silly mistake.

"I was reaching over for a water bottle to refresh myself, and Froome took advantage of this moment to attack," the Movistar rider said. 

"He went down, and got away from us, and took some seconds on all of us.

"I hope it's not decisive. I thought we could catch him on the descent, and Alejandro [Valverde], but it wasn't enough.

"Today was harder than we expected, and on the last part, I let my guard down.

"These are only the first mountain stages, and tomorrow will certainly be more decisive. I still have a lot of confidence."