Tim Wellens claimed victory on stage four of the Ruta del Sol to take the overall lead from Team Sky's Wout Poels, as Chris Froome suffered a puncture on Saturday's final climb.
Froome - competing for the first time since he returned an adverse analytical finding at last year's Vuelta a Espana - had already settled for merely attempting to aid team-mate Poels' bid for glory in Andalucia this week.
Yet the four-time Tour de France champion, who denies any wrongdoing in relation to his Vuelta doping test, was hampered towards the end of stage four and Poels also lost ground as Lotto Soudal's Wellens beat former Sky rider Mikel Landa (Movistar) in a cobbled finishing climb.
Wellens' stage win leaves him seven seconds clear of Landa heading into Sunday's final stage - a 14.2km time-trial that is likely to suit Froome.
Poels now occupies third place, albeit only 11 seconds off the pace, with the Astana duo of Jakob Fuglsang (+14secs) and Luis Leon Sanchez (+20secs) rounding out a tightly bunched top five.