Sergio Higuita claimed his first victory at a Grand Tour event after a superb solo ride on stage 18 of the Vuelta a Espana, as Primoz Roglic strengthened his overall advantage.
Higuita, 22, pulled clear at the front with around 50 kilometres to go and built up a sizeable lead in the mountainous 177.5km route from Colmenar Viejo to Becerril de la Sierra.
The Colombian stretched to 90 seconds in front until compatriot Miguel Angel Lopez led an attack along with Rafal Majka, Alejandro Valverde and GC leader Roglic.
Higuita's advantage was cut by over a minute but he was not to be denied a famous win, finishing 15 seconds clear as Roglic led the chasing pack over the line.
Roglic pipped Valverde in a sprint over the closing metres to pull further clear in the overall standings, with Quintana dropping to third behind his Movistar team-mate.
Lopez dug deep to attack again in the final climb but could not improve on fifth place, although it was enough to move top of the youth rider standings ahead of Tadej Pogacar.
Higuita was mostly out on his own in the final third of the race but showed redoubtable strength to keep out of reach of the strong quartet behind him, as Colombian fans roared him on from the roadsides.
Roglic was happy enough to move a step closer to glory in the capital after praising his Jumbo-Visma team-mates for their ride.
"It was another hard day and the team was super strong again," he said. "Today when Astana attacked in the penultimate climb, I was alone but Neilson [Powless] was up the front ready to wait for me. And in the end, it's on me. I also had good legs and we need to continue our good job.
"I don't expect any easy day. We're one day closer [to the victory in Madrid]. It was another hard day, another good day for me and my team. We can be optimistic and retain focus until Madrid."
1. Sergio Higuita (EF Education First) 04:33:09
2. Primoz Roglic (Jumbo-Visma) +00:15
3. Alejandro Valverde (Movistar) +00.15
4. Rafal Majka (Bora-Hansgrohe) +00.15
5. Miguel Lopez (Astana) +00:17
1. Primoz Roglic (Jumbo-Visma) 71:16:54
2. Alejandro Valverde (Movistar) +02:50
3. Nairo Quintana (Movistar) +03:31
1. Primoz Roglic (Jumbo-Visma) 137
2. Tadej Pogacar (UAE Team Emirates) 99
3. Alejandro Valverde (Movistar) 98
King of the Mountains
1. Geoffrey Bouchard (AG2R La Mondiale) 76
2. Angel Madrazo (Burgos BH) 44
3. Tao Geoghegan Hart (Team INEOS) 35
Friday offers the chance for the sprinters to take control of a race, as a flat 165.2km from Avila ends in a short climb over the cobblestones of Toledo.