Vuelta a Espana leader Joaquin Rodriguez stretched his lead over rival Chris Froome in the overall standings after finishing second to Alejandro Valverde on stage eight.
Spain clinched the top three places in the race's fourth summit finish on Saturday, with Valverde and Rodriguez followed home by another overall contender Alberto Contador as Britain's Froome struggled to maintain contact.
The leading trio dropped Froome in the final kilometre of the Collada de la Gallina climb in Andorra, just eight km long but made much tougher by constant changes of gradient of up to 20 percent.
Flailing wildly in the last 200 metres, Team Sky's Froome finished 15 seconds back. He retained his second spot overall, now 33 seconds behind Rodriguez and just seven ahead of third-placed Contador.
"Today was tough, I'm just glad I got through it without losing too much time," Froome told reporters.
"The time trial (on Wednesday) will be very important, but the three big mountain stages matter just as much," added the Olympic time trial bronze medallist.
Froome's team mates had laid down a devastating pace on the first segments of the narrow climb, which was packed with fans, and the Tour de France runner-up clawed his way steadily back up to initial attacks by Valverde and Rodriguez.
However, Froome could not respond when first Contador, then Valverde and Rodriguez, dropped him near the end.
"The four strongest riders in the race were all up there, but it's too close to say which of us is the best yet," Valverde, fourth overall, told reporters.
"One day it's me, the next it's Alberto or Froome. It's very close.
"I had made one attack to drop guys like Robert Gesink (fifth overall) I could see they were suffering.
"Rodriguez told me that the climb wasn't so hard near the top, and not to try to follow Contador when he made his attack but to go at my own rhythm.
"I followed his advice and followed him all the way to the finish. Then I sneaked past," added the 2009 Vuelta champion, who has won two summit finishes in the race this year.
Katusha's Rodriguez, now in the lead for a fifth day, thought his chances of winning the Vuelta depended on Wednesday's time trial.
"I have to be honest and say that my chances of success depends as much on me riding the time trial of my life next Wednesday as it does on Froome and Contador having really bad days," he said.
"They're both real Grand Tour specialists, whereas me and Alejandro are maybe better than them in other types of races like the world championships."
Sunday's stage takes the Vuelta peloton from Andorra on a 194-km ride to the Catalan capital of Barcelona prior to the race's first rest day on Monday.
The Vuelta finishes on Sunday Sept. 9 in Madrid.