Igor Anton's counter-attack on the ascent to Pal in the Pyrenees gave the Spanish climber his second solo win of the Tour of Spain and the overall lead.
Euskaltel-Euskadi rider Anton is 45 seconds ahead of compatriot Vicenzo Nibali in the overall standings.
Anton also took over as the leader of the sprint standings, with Mark Cavendish falling from first to third.
Manxman Cavendish finished stage 11 in 165th place and is 135th overall while Scot David Millar is in 87th place.
"I never came to this Tour to win, so losing won't be a disaster," stated Anton, who turned professional in 2005.
"I was feeling a bit rough on the final climb and so I played it very cool and hung back when the attacks started.
"At first I didn't count on a stage win, I just wanted to hang on to what I'd already got.
"But then halfway up I started feeling a lot better, and saw that other riders like Joaquim Rodriguez and Nibali were in trouble.
"So I got past them, and then managed to catch Ezequiel just in time to get the stage win."