Spain's Juan Jose Cobo powered away six kilometres from the summit of his country's toughest single climb, the Angliru, to claim victory in the 15th stage and the overall Tour of Spain lead.
After attacking where the single-track road looped its way up a mist-enshrouded cliffside, the Geox rider gained 48 seconds on Dutchman Wout Poels and Russia's Denis Menchov.
Nicknamed "the Bison", Cobo crossed the finish line on desolate moorland waving the little finger and thumb of his right hand like bison horns as a victory gesture.
Overnight leader Bradley Wiggins of Britain received strong assistance from Sky team mate Chris Froome but suffered on ramp-like slopes that rose over 23 percent in places.
With six stages left, Cobo leads by 20 seconds from Froome, with Wiggins now third overall at 46 seconds.