UAE Team Emirates rider Dan Martin won the 130-kilometre fifth stage of the Criterium du Dauphine on Friday, while Team Sky's Geraint Thomas took the overall lead from Italian team mate Gianni Moscon.
Ireland's Martin finished the stage with a time of three hours, 21 minutes and 19 seconds. He was four seconds ahead of Thomas, staving off a tough fight from the Briton in the final kilometre.
"These four days in the mountains are the hardest four days I would have raced I think in a one-week stage race," said the 32-year-old Thomas.
"It's a super hard climbing stage race, even harder on the weekend now. I'll enjoy tomorrow, or I'll try to enjoy it in the jersey and defend it but it's super hard."
Team Sky top the team standings for a third straight day with a combined time of 50 hours, 39 minutes and 47 seconds.
They are followed by AG2R La Mondiale who are eight minutes and 56 seconds behind.
The 110-kilometre sixth stage on Saturday will take place between Frontenex and La Rosiere Espace San Bernardo.