Sergio Henao retained the race lead at the Vuelta al Pais Vasco while Nairo Quintana won a difficult queen stage.
Henao benefitted from a brave effort from his Team Sky team-mates who gamely defended the yellow jersey despite a depleted squad of just six.
After fending off the mid-stage challenge of Peter Velits (Omega Pharma - Quick-Step) in the break the day came down to the famous final Arrate climb.
Henao and Richie Porte (Team Sky) combined to keep the pace high in the final kilometres, both riders doing enough to cement their overall positions of first and third respectively.
Quintana (Movistar) continued his impressive season by jumping clear in the final metres, taking the stage win and two seconds out of compatriot Henao on the downhill run to the line.
Alberto Contador (Team Saxo-Tinkoff) occupied third to stay level on time with Porte, an elite group swallowing up a dangerous late move from Simon Spilak (Katusha) on the first category Alto de Usartza.
Renowned for its wet weather, the Basque Country didn't disappoint on a tough queen stage featuring six categorised climbs over 151.6km.
Seven riders went clear as the race left Trapagaran - a significant break including the likes of Nicolas Roche (Team Saxo-Tinkoff), Andy Schleck (RadioShack-Leopard) and two team-mates of Samuel Sanchez, Egoi Martinez and Gorka Izagirre (Euskaltel-Euskadi).
Yet with some big teams represented the move was quickly shut down, Team Sky moving to control the pace on behalf of Henao as a tough day on wet roads began.
The race finally settled into a rhythm as five riders, including Velits and Eduard Vorganov (Katusha) (at the second time of asking) went clear to the tune of five minutes.
Team Sky bravely set about controlling the race - Jonathan Tiernan-Locke, Joe Dombrowski and Xabier Zandio combining to keep the break contained before handing over to Vasil Kiryienka.
The day's tough ramps saw the break split apart on the first category Alto de Isua with Velits, Daniele Ratto (Cannondale) and Matteo Montaguti (AG2R-La Mondiale) pushing onwards.
Movistar were the first of the lead teams to blink, finally taking it up with 25km to go on the penultimate climb of the Alto de San Miguel, the gap quickly falling with Velits no longer the leader on the road.
One by one more teams got involved as the stage win came into view to set up a flurry of attacks on the final climb - Spilak reeled in with two kilometres to go before Quintana claimed his second win of the season.