As we join the action with 150km to go in the stage, the attacks are coming thick and fast as riders fight to get in the break of the day.
The hilly profile of the stage makes it ideal for a breakaway, with the Astana team having little incentive to chase an attack. The hills also make it difficult for the sprinters' teams, meaning the right attack could be allowed to stay away.
Check out the profile of today's stage.
A group of 50 riders had opened a gap but the peloton has chased them down.
Sylvain Chavanel (IAM Cycling), Iljo Keisse (Etixx-Quick Step) and Jimmy Engoulvent (Europcar) opened a gap after 25km of fast racing but they were quickly caught.
It is time for the climbers to try to get in a move now as the peloton heads to the Alto Coolado de Oseja. It is 8.2km long but climbs at just 3.7%.
We have more attacks, with Sylvain Chavanel (IAM Cycling) gonig again, this time with Nelson Oliveira (Lampre - Merida) and Yukiya Arashiro (Europcar).
The average speed in the first hour was a painful 44.6km/h.
As we await the break of the day, its a good time to check out the other news of the day.
After the polemics and anger of the motorbike incidents, video footage of Sergio Paulinho's clash with a television motor bike has emerged thanks to Spanish television, the broadcaster for the race.
The latest accident sparked a lot of calls for improved safety, including one from the riders' CPA association president Gianni Bugno, who called for a special meeting with the UCI so "riders can explain their demands to finally stop this bloodbath".
From the Cyclingnews blimp we can see that Alessandro De Marchi (BMC) has joined the attack. The Italian has endured a difficult, injury-hit season with BMC but is back to his usual aggressive nature.
It seems the high pace is causing Nairo Quintana problems. The Colombian revealed he had a fever on the rest day and has struggled to recover. His race could be over.
120km remaining from 178km
Mikael Cherel (AG2R - La Mondiale), Jérôme Coppel (IAM Cycling), Ruben Plaza (Lampre - Merida) and Jelle Vanendert (Lotto Soudal) have also joined the attack. There are 14 riders up front now.
Ruben Plaza (Lampre-Merida) was the first to the top of the climb, taking the mountain points as he tries to take the blue polka-dot jersey from Omar Fraile (Caja Rural).
The peloton is only 20 seconds behind the attack.
Quintana is back in the peloton after some help from a teammate but the rides face more climbing before a long descent to the finish.
The Vuelta a Espana continues until September 13 but other riders will be in action elsewhere, with the Tour of Britain starting this weekend in Wales.
The attack has split under the effects of the climbs, with eight riders ahead. The chasers are at 20 seconds with the peloton at 45 seconds.
The peloton seems to have let the break go but now the chasers are trying to close the gap on the lead group.
110km remaining from 178km
The first category Alto de Beraton is causing the gap to open but also testing the form of the riders in the break.
However the peloton is now 2:30 back.
There a total of 23 riders in the break, which seems to be the move of the day.
Riders in the attack include Nicolas Roche, Segio Henao (Team Sky), Davide Arroyo (Caja Rural - Seguros RGA), Julien Simon (Cofidis), Kevin Reza (FDJ), Jose Joaquin Rojas (Movistar), Romain Sicard (Europcar) and Pawel Poljanski (Tinkoff - Saxo).
Steve Cummings (MTN Qhubeka) is also in the attack.
115km remaining from 178km
All the chasing riders are now in the front group, creating an attack of 24 riders. The peloton is at 3:00.
Other strong riders in the attack include Cameron Meyer (Orica-GreenEdge), Sylvain Chavanel (IM Cycling) and Alessandro De Marchi (BMC).
However the peloton seems scared of such a big group and is chasing the attack. The gap is down to 1:50.
Romain Sicard (Europcar) is the best placed rider in the attack. He is 6:41 behind Aru in the GC.
The high-speed is raking its toll on the riders with both Mattia Cattaneo (Lampre-Merida) and Mitchell Docker (Orica-GreenEdge) quitting the race.
100km remaining from 178km
The Astana team is keeping the attack under control with a steady chase. The gap is at 2:30.
85km remaining from 178km
with 93km covered and 85km remaining, the riders are half-way through the stage.
#LV2015 The lead group has grown to 24 (!) riders. @lampre_merida represented by @Nelsoliveira89, Rubén Plaza and @valerioconti93. #Great!
It is slightly cloudy in Tarazona, with lower temperatures after the heat of the opening 10 days.
The break is pushing ahead on the descent, with the peloton now at 4:15.
The wind could be a big factor in the finale today with a cross wind blowing at the finish.
The stage is also the last stage before yet more mountain finishes and the fight for the GC.
The peloton is lined out on the long highway, riding away from the dark rain clouds.
The wind is blowing from the right side of the road and so Astana is riding 'half road', putting much of the peloton into the road gutter and in the wind.
The wind is causing some tension and crashes. Iljo Keisse (Etixx - Quick Step) goes down after a probably touch of wheels but seems okay.
66km remaining from 178km
The peloton is lined out. Today is a transition stage but is going hurt.
Astana has five riders on the front, with another rider sat behind Aru, who is wearing the red jersey.
#LV2015: @NikiTerpstra & @glbrambilla remain in a 24-rider breakaway. 4’39” gap, 55.3km to go.
The riders are close to the intermediate sprint and the final Cat 3 climb of the stage. Both could inspire attacks to reduce the size of the 24-rider break.
The 24 breakaways are still working together, doing short turns on the front.
Gianluca Brambilla edged clear to take the intermediate sprint. That puts him ahead of Sicard in the general classification. However the break will need to finish 6:21 ahead of Fabio Aru for Brambilla to take the race lead.
We have the first attacks in the front group as some riders get frustrated at some riders for not working.
38km remaining from 178km
Monfort sparked a chase but now Poljanski of Tinkoff-Saxo is trying to go across to Chavanel and Oliveira.
The race is on a narrow country road, making attacks easier because the front group is lined out.
Poljanski is now out front alone and leads the race over the climb. But his gap is slim.
There is another little rise before a long descent towards Tarazona. However the final kilometres include some shorts climbs.
28km remaining from 178km
Were into the final 30km and we have more attacks. Oliviera is attack again. There 20km of fast descent now.
The peloton has eased off slightly, with the gap now at 4:30.
Oliviera is at the head of the race now after catching and passing Poljanski.
Oliviera is descending at 70km/h, using all the road in the corners.
Oliviera leads by 15 seconds.
20km remaining from 178km
Oliviera is giving it everything but the others are not letting him get away.
The two other Lampre riders are trying to slow the chase and jumping after other attackers.
Oliviera now has 30 seconds.
14km remaining from 178km
Oliviera is a good time trialist and using his skills to carve out a 40 second lead. It could be enough for him to win the stage.
Oliviera is the current Portuguese TT champion. He has surprised the other attackers and is on his way to victory.
The Lampre-Merida team car comes up to Oliviera as the gap hits a minute. The DS Orlando Maini shouts at him and bangs on the car door to encourage him.
9km remaining from 178km
The two other Lampre riders in the break are working to block any kind of organised chase.
8.6km to go. Gap going up, now 56”. Terpstra trying to get a more organized chase, but unsuccessful so far. 5’15” to peloton. #LV2015
Today was a classic transition stage but the fight for overall victory will kick off again at the weekend with a series of three mountain stages.
Saturday's 215km 14th stage starts in Vitoria and heads west to the mountain finish atop Alto Campoo- Fuente del Chivo.
The climb to the finish is 18km long at a steady 5.5%.
Other breaking news today is the selection of the US squads for the world road championships in Richmond. It is the first time that US riders get to compete at home in a road worlds since 1986, before most of them were born.
Click here for the full roster and quotes from the leading riders about racing for USA at home in the USA.
Thanks for joining us for today's live coverage.
We have a full stage report, photo gallery, news and interviews on Cyclingnews.
Join us tomorrow for more live coverage as the Vuelta heads into the mountains in northern Spain.
