Chris Froome suffered a setback on his La Vuelta title bid, losing ground to chief rival Vincenzo Nibali as Stefan Denifl handed Aqua Blue Sport their maiden stage victory.
Froome lost 42 seconds on Nibali with his lead over the Sicilian cut to one minute 16 seconds on the gruelling climb to Los Machucos in La Vuelta's 17th stage.
The Team Sky star was forced onto the defensive and could not stop Nibali cutting his lead, as the Bahrain Merida man powered to a fourth place finish.
Britain's Froome appeared well-set to complete his mission to land the demanding La Vuelta and Tour de France double ahead of Wednesday's action, only to see his sizeable lead hauled back somewhat.
Austria's Denifl boosted wildcard entrants Aqua Blue Sport with their first stage victory in a contest already beset by controversy for the Irish outfit.
An alleged arson attack destroyed their team bus after the 11th stage of the race, but Denifl put all that to one side to sweep to victory here.
Veteran star Alberto Contador powered into second place, trailing Denifl by 28 seconds, to cement fifth place in the overall standings of his final race before retirement.