Frenchman Bardet was among 18 riders who who attacked fewer than 10 kilometres into the 165.7km route, and was first over each of the day's first two climbs to assume the King of the Mountains lead.

Compatriot Nicolas Prodhomme of AG2R-Citroën Team made several attacks afterwards to force the pace, but Team DSM's Bardet caught him on the concluding Pico Villuercas ascent.

And after drawing level with Prodhomme with 6km of the gruelling 14.5km climb to the stage finish remaining, Bardet pushed on to earn a solo win.

The 30-year-old - a former mountains classification winner on the Tour de France - crossed he line in 4 hours 20min 36sec - a full 44 seconds ahead of Cofidis' Spaniard Jesus Herrada and Australian Jay Vine, riding for Alpecin-Fenix, who were second and third in that order.

It is Bardet's first Vuelta stage win.

Jumbo-Visma rider Roglič, the two-time defending champion from Slovenia, made up 20 seconds on Norway's Eiking and is now 1min 36sec back in third.

Intermarché-Wanty-Gobert Matériaux's Eiking also lost four seconds to Cofidis Frenchman Guillaume Martin in a fragmented finish, so his overall lead is down to 54 seconds.

Another mountain stage awaits tomorrow.