Pre-race favourite Nairo Quintana crashed out of the Vuelta a Espana on Wednesday before a thrilling battle between the remaining contenders on the climb to the summit finish of stage 11 at Santuario de San Miguel de Aralar.
While Astana's Fabio Aru took the stage win, Quintana's Movistar team-mate Alejandro Valverde led red jersey holder Alberto Contador (Tinkoff-Saxo) over the line in second and third.
Chris Froome appeared in danger of losing significant time as he was again off his game, but the Team Sky man dug deep and was just behind in fifth place to remain very much in contention in the GC standings as he moves up to fourth overall, one minute 21 seconds behind Contador.
Contador took over in the race leader's red on Tuesday's time trial, when Quintana suffered a dramatic crash to lose more than three minutes.
And the 25-year-old Colombian was in the wars again early on this 153.4kilometre stage from Pamplona, caught in an early accident in the peloton and taken to hospital, where he was diagnosed with a broken shoulder bone.
His Movistar team later tweeted: "Confirmation: @NairoQuinCo has suffered a displaced fracture in his right-hand scapula, will undergo surgery on Thursday (10am). #LaVuelta".
Quintana was one of several withdrawals after the crash, with FDJ's Thibaut Pinot - third in this year's Tour de France - joining BMC's Steve Morabito and AG2R La Mondiale's Maxime Bouet in pulling out.
After that drama, the stage was slow to develop with an early breakaway reeled in swiftly before Valverde led Contador over the first intermediate sprint with both men chasing bonus seconds.
A four-man group did eventually get away, and the presence of Sky's Vasil Kiryienka in the break suggested the team were trying to animate the race in different ways with Froome not yet having shown the same form as his rivals.
The Belarusian proved the strongest of the breakaway and one-by-one dropped the others to go more than two minutes clear, but riding away to victory proved beyond the 33-year-old as he was caught early on the final climb - a punishing 9.9km haul to the summit, averaging 7.5 per cent and reaching 14 per cent at its steepest points.
That is when the action really began with Sky setting the pace on the front through Philip Deignan and Dario Cataldo, but it seemed they were going too fast for their own leader with Froome struggling to stay on the back of the leading pack.
Giant-Shimano's Warren Barguil moved off the front with 6.5km to go and from then on there were a series of punches and counter-punches with Contador, Valverde and Joaquim Rodriguez (Katusha) trying to cover every move.
Garmin-Sharp's Dan Martin was also active, but the Irishman's bid to break free 4km from the finish was swiftly reined in.
Froome had looked to be struggling but with two kilometres to go he drew alongside the leaders and briefly kicked forward, out of the saddle with the gradient hitting 14 per cent, to draw a swift response as the riders fought their way through the crowds on the narrow road.
That was the moment for Aru to attack, a reminder of why the Italian was considered a GC threat prior to time losses last week, and he was allowed to pull away with Contador and Valverde now more concerned with each other.
Aru could celebrate as the battle raged, with Valverde, Contador and Rodriguez crossing as a group six seconds behind him, and Froome rolling home one second further back.
With bonus seconds from the sprint applied, Contador lead Valverde by 20 seconds, with Froome moving up to fourth even as he concedes another three seconds to Contador to sit 1minute 21seconds back.
Former Team Sky man Rigoberto Uran, now of Omega Pharma-Quick Step, is in third, 68 seconds down on Contador, with Rodriguez fifth, 1min 35sec back.
Aru's win means he is seventh, 2min 13secs back.