Ben O'Connor's team has controlled stage 12 of La Vuelta a Espana, enabling the Australian rider to complete a week in the leader's red jersey.

The Perth cyclist has been in red since his epic solo breakaway win on stage six and his team ensured there would be no repeat of Wednesday's loss of 37 seconds to his nearest pursuer, Primoz Roglic.

Riding for long periods at the head of the peloton they were happy to allow a 10-man breakaway — which did not feature any general classification contenders — to escape, but kept close tabs on Slovenian Roglic and other threats.

Even after Pablo Castrillo rode clear to clinch an unexpected victory on Thursday, and the rest of the breakaway had come in, O'Connor kept his guard up, crossing the line in 14th, just behind his faithful teammate Felix Gall, to the fore of the peloton.

"It was a tricky start, it was actually really hard. And then we just controlled the race, made some pace on the final climb," said O'Connor, whose lead remains three minutes and 16 seconds.

Castrillo, 23, moved ahead towards the end of the 137.5km stage with a stunning attack amid mountainous terrain in north-west Spain, and had established a half-minute lead with 4km to go.

He maintained a gap throughout the final part of the brutal ascent. In the last 100 metres, realising he would secure his first Grand Tour stage win, he broke into a smile.

"The breakaway was very hard to make. The other guys were very strong. I was nervous for the finale but I decided to attack on the flat and it led me to the stage victory," the Spaniard said.

It was an emotional win for the Kern Pharma team, coming a day after their founder, Manolo Azcona, died aged 71.

Britain's Max Poole edged ahead of the chasing group in the final moments to secure second place, following Wednesday's third, while Spain's Marc Soler took third.

Tonight's 176km stage is another challenging one, finishing on the Ancares Mountain Pass. The final ascent is 7.7km in length with an average incline of nine per cent, which at times is 15 per cent.

AAP