Five blistering attacks by Spain's Alberto Contador on the emblematic Lagos de Covadonga climb failed to dislodge the Tour of Spain leader and compatriot Joaquim Rodriguez from the race's top spot on Sunday.
At the head of the race, Spain's Antonio Piedra from the low-budget Caja Rural team secured the biggest win of his career from a day-long break of 10 non-favourites overall.
Meanwhile, in the battle between the main contenders on the 13-kilometre climb, Contador tested Rodriguez's strength but failed to make the race leader crack.
"I wasn't feeling great this morning but then I realised other people could be feeling even worse than me, so I gave it a go," Contador, who finished 13th on the stage in the same time as Rodríguez, told reporters afterwards.
"You never know when your rivals are going to have a bad day," he added.
"Just as well he felt bad, because I couldn't have handled a bigger attack than those ones, I was really suffering," Rodríguez said.
"I lost count of the number of attacks he made - 32,33? If he's feeling better tomorrow then it's going to be very difficult."
Overall, Rodríguez's lead of 22 seconds over Contador remains intact, whilst a third Spaniard, Alejandro Valverde, moves onto the provisional podium in third spot, 1 minute 41 seconds back, as Britain's Chris Froome cracked half-way up the climb and slid to fourth overall.
"I'm not sure where I'll finish in Madrid, but I'll continue to try to do my best, I can't do more," Froome, a runner-up in this year's Tour de France, told reporters.
Piedra, 26, said he was delighted to win on one of cycling's most mythical climbs deep in the Pico de Europa region, and home to some of the last wolves in Europe.
The 2009 Tour of Portugal stage winner broke away from a break of 10 riders with 10 kilometres to go, to claim the victory on the race's eighth of ten summit finishes.
"My legs felt good and I went for it," Piedra said afterward, "this is one of those stages that you never forget no matter how much it hurts to win."
France's Ruben Perez finished second, two minutes and two seconds down on the Caja Rural rider, with France's Lloyd Mondory in third.
Monday sees the peloton tackle the third of three straight summit finishes, the 19.4-kilometre Cuitu Negru climb in Asturias.
The Tour of Spain finishes on Sept. 9 in Madrid.