A dramatic last 10 kilometres reached its climax when Geniez (AG2R), held off a late push for the line from Team Sky´s Dylan van Baarle, with Mark Padun (Bahrain-Merida) third.
"I didn’t plan to be at the front," Geniez said. "I thought Bora would control the stage for Sagan. And then we saw Formolo attack, there were about 15 riders at the front so I thought I had to go.
"We worked well together to quickly open a gap. Nibali was the main figure at the front, everybody was looking at him. Then, I had to be careful when attacks started. I wanted to wait for the sprint because I figured it was my best chance. The team is having a great start of La Vuelta. Tony (Gallopin) is still in a good position on GC and we’ll keep going until Madrid.”
Geniez, van Baarle were also involved in a crash immediately after crossing the line. The pair collided with a race official who was not looking where he was going. BMC's Dylan Teuns was also caught up in the crash. Cycling Central understands the race official is OK and van Baarle suffered cuts and bruising to his right hip, elbow and ribs.
The general classification
Yates (Mitchelton-Scott), who had worn the red jersey since stage nine, drops to second in the general classification after Herrada (Cofidis) formed part of an 18-strong breakaway group during the climb of Alto de Cadeira.
Together with Movistar pair Alejandro Valverde and Nairo Quintana, Yates allowed the gap to exceed 11 minutes and when they finally made their move, it was too late to hold red.
At the end of a twisting route between Mondonedo and Manon, Herrada leads Yates by three minutes and 22 seconds, with Valverde one second back in third.
"It is hard to believe," Herrada said. "In the end to take the lead is a dream, I couldn't challenge for the stage because I was exhausted but it is reward for the work we have been doing for a long time.
"I don't think about the podium now but I'll take it day by day and at least we have achieved this."
It was Geniez's third stage win at the 'Vuelta', after previous triumphs in 2013 and 2016.
"It's a relief," Geniez said. "The pleasure of winning is days like these when we just ride a bike after training hard and making sacrifices all year long.
"We attacked a lot towards the end of the stage. There was nothing in it on the line. It was a very special sprint."
The race continues with the 13th stage, stretching 174.8 kilometres between the town of Candas and La Camperona featuring a super tough finale to the finish.