Spaniard Joaquim Rodriguez closed to within one second of Vuelta leader Fabio Aru when he stormed clear on the punishing summit finish to win the 15th stage.
Katusha rider Rodriguez timed his late burst to perfection to beat Poland's Rafal Majka (Tinkoff-Saxo) into second place by 12 seconds, with Rodriguez's team-mate and compatriot Daniel Moreno a further two seconds back in third.
Italian Aru (Astana), who led Rodriguez by 26 seconds overnight, crossed together with Colombian Movistar rider Nairo Quintana one second behind Moreno after the 175.8-kilometre slog from Comillas to Sotres.
Dutchman Tom Dumoulin (Giant-Alpecin), who is expected to put in a strong performance in Wednesday's time trial, remains one of the favourites for overall victory despite finishing 51 seconds down in 12th and slipping to fourth overall.
With six stages remaining, Aru retains the leader's red jersey ahead of Rodriguez, with Majka and Dumoulin just under one and a half minutes behind in third and fourth respectively.
Ireland's Nicolas Roche has dropped four places in general classification to 21st.
"I worked really well on the stage and I enjoyed it a lot," said Rodriguez, who secured a ten-second bonus for the stage win.
"He (Dumoulin) has been pretty quick in the mountains so maybe he won't be so fast in the time trial, we don't know," added the 36-year-old.
"Dumoulin is in contention. Each day he is losing some time but what we don't know is if he is holding back on purpose. Maybe the lad is more intelligent than we think."
Today’s 15th stage was the second of three consecutive summit finishes in the three-week race, which ends on 13 September in central Madrid.
Riders face another tough test tomorrow with a 185-kilometre trip from Luarca to Ermita de Alba, which includes seven punishing climbs, and Dumoulin will need another good day in the mountains if he is to stay with the leaders.