Wout Poels remains in contention to win Ruta del Sol despite losing his lead on Saturday's gruelling finish in Alcala de los Gazules.
The Team Sky rider finished fourth on stage four, 13 seconds behind new overall leader Tim Wellens, and will have to make up 11 seconds on the Lotto Soudal rider on Sunday's time-trial finale.
Saturday's stage featured two big climbs, but they were taken at a more sedate pace with Andrey Amador (Movistar) and Sep Vanmarcke (EF Education First-Drapac p/b Cannondale) coming away from the break to lead into the final 5km.
However, they were picked up by the thinned-out peloton with just over 1km remaining, with Team Sky having lost Chris Froome from the lead group a few moments earlier because of a puncture.
Froome would eventually cross the line nearly 90 seconds behind Wellens who, along with Mikel Landa, took the initiative once the final, short but very sharp, climb began.
Poels was caught out by the acceleration but dug in well to pass a number of riders and keep his hopes of regaining the red jersey alive.
Wellens, meanwhile, went head to head with former Team Sky rider Landa on the cobbled finish and showed the better turn of pace on some of the steepest sections of the race.
He would eventually cross the line five seconds ahead of the Spaniard, with Jakob Fuglsang a further seven seconds down, just ahead of a rallying Poels.
Wellens will, therefore, have a seven-second advantage on Landa when he starts Sunday's 14.2km time-trial, which starts and finishes in Barbate.
Poels sits third overall, 11 seconds down, with Astana pair Fuglsang (+14s) and Luis Leon Sanchez (+20s) rounding out the top five.