Quintana took seven seconds back from Aru to move into ninth on GC. Aru still leads but saw his lead cut by one second to 26 seconds over Rodriguez, while Dumoulin drops to 49 seconds but stays in third.
Vitoria-Gasteiz - Alto Campoo
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We'll have to wait until the dust settles and the metaphorical mist clears before we can understand the bigger picture. Dumoulin crosses the line around 25 seconds down on Aru it seems.
It's hard to see what's happening because of the mist. Aru will lose a few seconds to his rivals but not much.
Valverde is leading a chasing group that includes Dumoulin and Meintjes.
Quintana and Rodriguez have attacked to distance Aru.
Back with the main favourites and Aru and Quintrana have been caught by the likes of Rodriguez, Pozzovivo, Chaves and Majka.
That's De Marchi's second win on the Vuelta in as many years.
Victory for Alessandro De Marchi of BMC.
Visibility is next to nothing thanks to this mist...
Nieve has attacked from the chasing pack. Dumoulin has cracked, apparently.
We have no idea how far Puccio is behind De Marchi because we have no helicopter shots - it's just too misty.
De Marchi is out of the saddle and riding to a second career win on the Vuelta.
Quintana is the only rider who can keep up with Aru back with the favourites.
De Marchi drops Puccio...
De Marchi and Puccio are leading as they approach the final kilometre...
Back with the main pack, Aru bounds clear himself - sparking a response by a handful of riders, including Quintana.
Now De Marchi steps on the pedals and bridges the gap before riding past Rojas and in pursuit of compatriot Puccio.
This is the steepest part of the climb, but they're really playing about - it's a game of cat and mouse out thre. Then Rojas goes! Puccio responds, but Cherel, De Marchi and Quintero struggle.
Cherel is caught as the leaders hit the wall of mist ahead of the 2-to-go barrier.
Another attack from Cherel, who opens up a small gap.
Puccio has managed to ride back to the other four riders. Cherel was reeled in after De Marchi's response.
The pace is up in the pack with Astana and Giant dishing it out. The gap is 5:45 so it's too late for the win...
Now De Marchi goes! The Italian lets rip from out of the saddle, taking Rojas and Quintero with him. Puccio has no answer.
ATTACK: Cherel is the first of the escapees to make his move. No response from the others, with De Marchi looking very disinterested at the back.
Bespectacled Spaniard Angel Madrazo is caught after his pointless kamikaze break.
The pace is not so fast so perhaps we won't see many fireworks today. All in all, it's a bit sedate. Very misty at the finish - the riders will reach that blanket in a couple of kilometres.
It's now Luis Leon Sanchez of Astana who is driving the pace in the pack as numerous riders are shelled off the back. No move in the break yet, who contineu to ride as one. The gap is down to seven minutes now.
Two Italians, a Frenchman, a Spaniard and an Colombian still have eight minutes over the pack. At some point soon, one of them will try his luck. It's the calm before the storm...
Movistar are setting the tempo on the front of the pack through Andrey Amador. They have five riders on the front - including Valverde and Quintana - ahead of the Astana team-mates of Fabio Aru.
God knows what Madrazo is up to attacking. He's no threat on GC and he has no chance of catching the break. Why not wait until one of the next two summit finishes?
The polka dot jersey Omar Fraile is in the gruppetto - but he won't be too bothered because most of the KOM points will be swallowed up by the break. Unless he fails to finish, the Spaniard will retain his jersey for another day.
The peloton has already split in two with a self-enforced gruppetto forming. A Caja Rural rider has jumped clear of the main pack - it's Angel Madrazo.
The break are still sharing the load out equally. It's a bit early for someone to go for a long-pop just yet - but expect De Marchi to roll the dice at some point. The gap is down to 8:40 but it's still going to be a two-race finale: for the stage and for the GC.
Sky have come to the front now alongside Astana - their man for the GC in the absence of Chris Froome is Mikel Nieve, who is currently 1:58 down in eighth place.
The leaders are onto the final climb, the HC Alto Campoo - a 18km climb that is not that steep, peaking out at only 9%.
That final climb looms with the gap still a rather large 9:30.
Astana now driving quite a fast pace alongside Movistar and Tinkoff-Saxo. The climbers will look to put Tom Dumoulin - the danger man for the ITT on Wednesday - in trouble today. Remember, Rafal Majka is in fourth place and the Pole is a tidy climber. Cannot be discounted...
It was that man Quintero who won the intermediate sprint ahead of De Marchi and Puccio but it was hardly contested.
The final rider in this break is Colombian Carlos Quintero, who has a reputation as something of a breakaway specialist. The 29-year-old is riding his third Grand Tour and his first Vuelta after two rides in the Giro. He hasn't finished higher than 49th place in this year's race, so he looks set to change that today. But can he net his first ever pro win?
Spanish national champion Alejandro Valverde is currently been paced back into the peloton by three Movistar team-mates after picking up a puncture.
This is Salvatore Puccio's fifth Grand Tour and second Vuelta and the 26-year-old Sky domestique is still looking for a maiden pro win. Puccio has been at Sky all his career and his best result so far this season is second place in the opening prologue time trial in the Tour de Slovenie in June.
The gap is back up to 9:30 for the five leaders, who will very much contest the victory today.
Frenchman Mikael Cherel, 29, is riding his fourth Vuelta and his ninth Grand Tour. Should this break go the distance he'll have his best ever stage finish on a major race: his current zenith is 6th (in both the 2009 and 2013 Vueltas). The former FDJ rider is looking for his first ever pro win, although this July he finished an impressive 18th in the Tour de France - his best ever Grand Tour final placing.
Rojas is picking up gels from his Movistar team car. He's still bearing the scars from that nasty fall he suffered on a descent last week.
Fabio Aru is currently off the back of the peloton after stopping off for a call of nature. There's no hurry for the peloton, which seems content to roll along and let this break continue battling for the stage win further up the road.
The five-man break still has 8:30 over the pack so the smart money is on them winning. Of the five leaders there's one man who really stands out - although don't discount that man Quintero - Team Colombia need a win...
The riders are onto a plateau ahead of the intermediate sprint. It looks like the action will all come down to the final climb with regards to the GC battle.
The peloton still tackles the climb with the Astana team of Fabio Aru setting a gentle tempo.
The break crests the summit of the Puerto del Escudo with a lead of nine minutes. Cherel once again takes maximum points. That will put him onto 15 points for the day, which is fifth place in the KOM standings overall.
Third rider to withdaw today: Lluis Mas (Caja Rural - Seguros RGA).
An idea of the kind of scenary out there today, thanks to Eurosport's very own Laura Mesequer...
The most experienced rider in this group is Jose Joaquin Rojas who, like De Marchi, was involved in yesterday's break. The Spaniard from Movistar is riding only his second Vuelta, although he has ridden the Giro once and the Tour on six occasions. Always there or thereabouts in the sprints, Rojas has yet to finish first or second on a Grand Tour stage, with many, many 3rd, 4th and 5th places to his name. His last pro win - the eight of his career - came in the Tour of Qatar back in February.
Alessandro De Marchi is the only rider in this break to have tasted victory on the Vuelta, the Italian having won stage 7 to Alcaudete last year. The 29-year-old climber also has a win in the 2013 Criterium du Dauphine to his name and this is his sixth Grand Tour (with two appearances in each so far). De Marchi was involved in yesterday's break but missed a trick when Nelson Oliveira attacked on the final descent.
The break is onto the Cat.1 Puerto del Escud, which is almost 12km long and peaks out at 15%.
A reminder of our five leaders, who have been out since the 52nd kilometre: Alessandro de Marchi (BMC), Salvatore Puccio (Team Sky), José Joaquín Rojas (Movistar), Mikael Chérel (Ag2r-La Mondiale) and Carlos Quintero (Team Colombia). The gap is 9:55.
The gap is approaching ten minutes now for the five leaders as they near the end of this short but sharp technical descent. It will head up almost instantaneously for the second of today's categorised climbs.
Movistar's two leaders have been in the wars, what with Quintana's illness and Valverde's shoulder injury following his crash last week. They're 3:07 and 1:52 down on Aru on GC. Movistar team director Jose-Luis Arrieta told lavuelta.com: "We have three very hard days ahead of us and we're not in an ideal position. But we've had a great season so far and we can't complain. We're happy that Nairo was able to overcome his problems yesterday. He struggled in the first climb but then managed to stay in the bunch. We hope his virus is over now. We'll see today. If he manages to stay with the best, then we have great hopes for the end of the Vuelta. Alejandro's shoulder is still stiff in the morning but it goes better during the stage."
For laptop, tablet and PC users, here's what the riders have to expect in the final 2km today. It's misty up there and it's currently only 14 degrees Celsius.
Like all the other nine summit finishes on this year's Vuelta, the Alto Campoo is being used for the first time as a stage finish. It has featured three times before on the Vuelta, mind: in 1985, 1987 and 1993.
The gap increases to over eight minutes for these escapees, all of whom can dream of a victory today atop the Alto Campoo.
It's that man Cherel who takes 5pts for crossing the summit in pole position, with Rojas second with 3pts and Puccio third for 1pt. None of these men are a threat to the current polka dot jersey, Omar Fraile of Caja Rural. The Spaniard had 55 points, with Ruben Plaza (Lampre-Merida) in second place on 27 points and a third home rider, Astana's Mikel Landa, on 25 points.
The best placed rider in this break is Frenchman Cherel, who is a full hour down on Aru on GC and so there's no panic from Astana whatsoever. Remember, Aru leads Joaquim Rodriguez by 27 seconds in the overall standings with Dutchman Tom Dumoulin in third a further three seconds back.
The leaders are onto the Cat.3 Puerto Estacas de Trueba. Andrei Zeits and Alessandro Vanotti set the tempo back on the front of the peloton for their Astana team-mate Fabio Aru, the red jersey.
We join the race ahead of the first categorised climb and that break of five riders now has six minutes to play with over the peloton.
After another attack by Alessandro De Marchi (BMC) a small group formed featuring Salvatore Puccio (Sky), Mikael Cherel (AG2R-La Mondiale) and Carlos Quintero (Colombia), with Jose Joaquin Rojas (Movistar) in pursuit.
One rider particularly eager to be part of the break today has been Alessandro De Marchi (BMC). The Italian was in an early nine-man attempt and has been trying his luck throughout a fast opening hour of racing during which 46km were covered.
Thomas De Gendt (Lotto Soudal) joins Sanchez as a DNF today.
Samuel Sanchez (BMC) withdrew from the race early today after struggling to keep in touch with the pack. BMC have had a fairly rotten race since winning the opening time trial in Marbella, the nadir being the abandonment of their leader Tejay Van Garderen.
Numerous attempts were made to form an early break - all thwarted by the bunch over the undulating opening section of this stage.
170 riders took to the start in Vitoria for the longest stage of this year's Vuelta a Espana.
One non-starter today: Geoffrey Soupe (Cofidis).
Yesterday we witnessed a Lampre-Merida master-class as Portugal's Nelson Oliveira won from a large break of 24 riders that also included two team-mates. There was no change at the top of the standings, but Nairo Quintana was edged out of the top ten by Gianluca Brambilla and Romain Sicard, who both starred in the break.
Hola and welcome to live coverage of stage 14 of the Vuelta a Espana - a 215km ride into the Cantabrian mountains that featured three categorised climbs including the summit finish atop the Alto Campoo at Fuente del Chivo.