Ecuadorian Richard Carapaz said it will be a "luxury" to defend the Vuelta a Espana's red jersey after taking the race's overall lead while Spaniard Ion Izagirre won Sunday's sixth stage.
Former Giro d'Italia winner Carapaz overtook defending champion Primoz Roglic who struggled in wet conditions in Pyrenees.
Ineos' Carapaz, 27, made the most of Roglic's tough day in the mountains to take an 18-second lead as the Slovenian fell to 30 seconds behind in fifth.
"We have done very well, and this is the reward for the whole team," Carapaz said, on the day that another Ineos rider, Tao Geoghegan Hart won the Giro d'Italia.
"There were many attacks. I had calculated the distance and I attacked at the right time," Carapaz said. "There is still a lot of the Vuelta and we are going to defend it, it is a luxury to be able to defend it."
Canadian Michael Woods of Education First finished second with Portuguese rider Rui Costa of UAE Team Emirates third behind 31-year-old Izagirre.
The stage was rerouted because the scheduled finish at 2,115m on the Col de Tourmalet meant crossing into France and was moved south of the border due to the coronavirus pandemic, ending instead at 1,790 metres at the Formigal.
After a series of attacks a break of more than 22, including brothers Ion and Gorka Izagirre of Astana, had solidified with 120km left.
Carapaz, Jumbo-Visma's Roglic, who had led since Tuesday's opening stage, and the peloton gradually lost time through two category climbs and an intermediate sprint just across the French border.
Temperatures dropped to 13 degrees celsius and two-time Vuelta winner Chris Froome ferried cold weather gear to his Ineos team-mates, including Carapaz.
With 3km to go, Ion Izagirre made his attack through thick fog and heavy rain at more than 1,700m to add to his stage wins at the Tour de France in 2016 and the Giro four years earlier.
Roglic, covering his red jersey with a black jacket, struggled up the final climb to the Aramon Formigal ski resort and could not respond when Carapaz accelerated. Briton Hugh Carthy of Education First went with the Ecuadorian and moved to second overall.
Carapaz leads Carthy by 18 seconds, Irishman Dan Martin of Israel Start-Up Nation is third a further two seconds back. Roglic is fourth 30 seconds off the lead.
Monday is the first rest day. Tuesday's 159.7km hilly stage seven starting in Vitoria in the Basque Country.