Four-time champion Primoz Roglic finished fourth on stage 18 but only cut his overall deficit to Enric Mas by 33 seconds, leaving the Spaniard with one hand on the Vuelta a Espana trophy with just three stages remaining.
None of the riders in the general classification top 10 had ever beaten Roglic in a time trial and that remained the case at the end of the day in Jerez de la Frontera.