Italian Vincenzo Nibali clung on to his narrow lead of the Tour of Spain after a gruelling 18th stage on Thursday.
Sky's Belarusian rider Vasil Kiryienka won the stage after breaking away at the end of the 186.5km ride from Burgos to Pena Cabarga that featured five categorised climbs, including a tricky final ascent.
Kiriyenka's breakaway to the summit of Pena Cabarga almost cost Nibali his lead atop the general classification, now cut to just three seconds.
The Sicilian couldn't respond to a push by the Katusha team in the final ascent, and then the attack by RadioShack's 41-year-old American rider Chris Horner, who was sixth across the finish line.
Nibali, who finished 10th 25sec off Horner, also gave away time to Spaniards Alejandro Valverde (Movistar), now third in the overall standings at 1:10, and Joaquim Rodriguez (Katusha), fourth at 2:24.
"Horner is very strong, it's incredible what he's doing at almost 42 years of age," Nibali told Spanish television at the end of the race.
"Horner showed he's one of the great pretenders for this Vuelta."
Kiryienka, who bowed out of the Tour de France in July after missing the time cut on stage nine in the Pyrenees, was one of an initial 15-strong group to break away from the main peloton, and attacked in Alto del Caracol, 45km from the finish.
The 32-year-old arrived at the foot of the Pena Cabarga with 1:30 on his rivals and managed his ride-in to perfection.
Friday's 19th stage sees the riders tackle 181km with the finish again at altitude, demanding a first-category climb to Alto del Naranco before tackling the infamous Alto de l'Angliru on Saturday's stage.