Behind the breakaway battle, Enric Mas resisted the late pressure from Primoz Roglic, Felix Gall and Richard Carapaz. Oscar Onley lost contact as the leading GC quartet traded accelerations, while Mattias Skjelmose had already been distanced by an attack from the red jersey.
Buitrago cannot shake Brenner
Mario Aparicio had looked capable of delivering a major home victory after attacking as two groups of breakaway survivors merged with approximately five kilometres remaining.
The Burgos Burpellet BH rider built an advantage of around 40 seconds, but Buitrago, Brenner and Rodriguez rapidly emerged as his principal pursuers. Paret-Peintre also moved towards the front as earlier attackers Georg Steinhauser and Joao Almeida faded.
Buitrago reached Aparicio on a ramp touching 16 per cent with around 3.5 kilometres remaining and immediately attempted to distance Brenner. The German initially appeared to be slipping away, but limited his losses and returned to Buitrago with two kilometres left.
Rodriguez and Sosa then joined them to create a four-rider contest beneath the flamme rouge. Sosa attacked on the final steep section without escaping, before Buitrago made a more damaging acceleration and again opened daylight.
Brenner was the only rider capable of responding. He closed the gap before the road eased and used his superior finish to complete an unlikely comeback metres from the summit.
Vermaerke shapes the stage from 50 kilometres out
The winning group emerged from a 44-rider breakaway formed after a frantic opening in which several sizeable moves were neutralised.
UAE Team Emirates – XRG placed Almeida, Kevin Vermaerke and Ivo Oliveira in the escape, while Movistar sent Pablo Castrillo and Raul Garcia Pierna ahead as possible support for Mas. Buitrago, Pello Bilbao, Paret-Peintre, Filippo Zana, Lorenzo Fortunato, Steinhauser and Sosa supplied much of its climbing strength.
Vermaerke attacked on the descent from the Puerto de los Villares with more than 50 kilometres remaining, taking advantage of the poor cooperation inside the oversized group. The American built a lead of 1:45 and reached the Puerto de Locubin with the peloton approximately seven minutes behind.
He retained 45 seconds at the summit after taking maximum mountain points, but Steinhauser overhauled him on the short Muur van Valdepenas. Guillaume Martin-Guyonnet and Aparicio later joined Steinhauser before Zana and Brenner crossed to the front during the opening half of La Pandera.
Vermaerke attempted to revive his challenge after being caught, but the steep and constantly changing gradients progressively reduced the enormous break to the riders who would contest the finish.
Mas answers late GC pressure
With the escape holding more than seven minutes at the foot of La Pandera, the stage victory and GC contest unfolded separately.
Mas reached the decisive gradients with Ivan Romeo as his final Movistar teammate, while Castrillo and Garcia Pierna remained further up the road as satellite riders. Once Romeo finished his work, Mas made the first meaningful acceleration among the favourites with 2.7 kilometres remaining.
That move dropped Skjelmose before Roglic moved to the front. Carapaz then increased the pressure and succeeded in distancing Onley, who had started the day fifth overall and only 30 seconds ahead of white jersey rival Jakob Omrzel.
Roglic delivered another measured acceleration inside the final 1.5 kilometres, but Mas, Gall and Carapaz remained with him. Gall also tried to create separation late on without dislodging the other three.
Brenner’s victory settled a dramatic contest at the front, while Mas emerged from another major mountain examination still alongside his three closest challengers on the road.