Antonio Piedra climbed to a surprise win in the 15th stage of the Vuelta a Espana, while fellow Spaniard Joaquin Rodriguez kept the overall race lead.
Chris Froome endured a tough day and finished 35 seconds behind Rodriguez to slip to fourth in the standings.
Alejandro Valverde replaced British rider Froome in third place overall.
"It was a really tough climb. I'm really suffering, I'm just trying to do as much as I can," said Team Sky rider Froome, who finished in 23rd place.
"I'm suffering in the mountains against the Spanish riders. I'm just trying to stay up there. I'll do the maximum possible and be happy with that."
Piedra dominated the 186.5km (115.9-mile) stage from La Robla to Lagos de Covadonga, claiming the greatest win of his career to date, eclipsing his success in stage five at the Tour of Portugal in 2009.
France's Ruben Perez came second, trailing the Caja Rural rider by two minutes and two seconds, with France's Lloyd Mondory in third.
Katusha rider Rodriguez was engaged in a cat-and-mouse battle with red jersey rivals Alberto Contador and Valverde up the gruelling 13km climb to the peak of Lagos de Cavadogna which ended the stage.
Despite repeated attempts by all three men to break away, with Contador the most active agressor, they finished together, with Valverde of Movistar just fractionally ahead in 11th spot.
Rodriguez was a bike's length ahead of Saxo Bank's Contador, who remains 22 seconds behind his fellow Spaniard, in second place overall.
Stage 15 results
1. Antonio Piedra (Spa/Caja Rural) 5:01:23"
2. Ruben Perez (Spa/Euskaltel) +2:02"
3. Lloyd Mondory (Fra/AG2R)
4. David De la Fuente (Spa/Caja Rural)
5. Pablo Lastras (Spa/Movistar) +2:07"
General classification after 15 stages
1. Joaquin Rodriguez (Spa/Katusha) 58:17:21"
2. Alberto Contador (Spa/Saxo Bank) +22"
3. Alejandro Valverde (Spa/Movistar) +1:41"
4. Chris Froome (GB/Team Sky) +2:16"
5. Daniel Moreno (Spa/Katusha) +4:51"