It took almost 60km of racing before Alessandro de Marchi (BMC Racing), Salvatore Puccio (Team Sky), José Joaquín Rojas (Movistar), Mikael Chérel (AG2R) and Carlos Quintero (Colombia) broke away from the peloton - establishing a ten-minute lead over the peloton before the final climb.
It was effort well spent for de Marchi, however, as the BMC Racing rider ultimately took the win after attacking with 2km to go as thick fog descended over the summit of the Alto Campoo.
Despite a flurry of activity in the finale the general classification was largely unchanged, though the time gaps to race leader Fabio Aru (Astana) narrowed slightly. He now leads the general classification by 26 seconds ahead of Joaquim Rodriguez (Katusha), with Tom Dumoulin (Giant-Alpecin) at 49 seconds.
"With a bit of luck, in the right moment, I had the energy to do a fast attack," de Marchi said. "I was lucky because I do not think I was the strongest."
"I didn't expect this before the beginning of the Vuelta, and I expected it even less before this stage," he added. "I had given so much yesterday that i was not sure what I could do today. It was diffiuclt because everyone rode against me."
How it happened
The race progressed steadily for the majority of the 215km from Vitorio to the summit of Alto Campoo but became animated with 4km to go.
Chérel was the first of the break to attack, but was wound back before de Marchi made his decisive move.
At the same time, further down the mountain, race leader Aru launched an attack with only Nairo Quintana (Movistar) able to match his pace. Puccio and Rojas followed de Marchi over the line, with Cherel and Quintero behind, as the rest of the general classification contenders kept their cool and worked together to contain the damage.
They finished within seconds of each other, with Quintana the first of the favourites to arrive home 3min 32 sec behind de Marchi, and just five seconds ahead of Rodriguez, Esteban Chaves (Orica-GreenEDGE) and Aru.
Dumoulin, Alejandro Valverde (Movistar) and Rafal Majka (Tinkoff-Saxo) all lost time to Aru, while Quintana, Rodriguez and Chaves looked impressive with two more summit finishes on the cards over the next two days.
It is likely the climbing specialists will seek to take time on Aru before Tuesday's rest day, while time trial specialist Dumoulin will look to limit his losses ahead of Stage 17's 38.7km race against the clock in Burgos.