Daniel Diaz (Funvic) enhanced his overall lead at the Tour de San Luis with his second stage win in the opening four days of the race.
The Argentinian national champion took the race's first mountain stage to win atop Alto El Amagro.
Alex Diniz (Funvic) took second, while Rodolfo Torres (Colombia) came in third.
A four-man break - Dario Díaz (San Juan), Juan Arango (Colombia), Juan Valencia (Team Colombia), and Giacomo Berlato (Nippo-Vini Fantini) - went clear early in the stage and at one point gained an advantage of nearly seven minutes over the peloton.
At the foot of the monstrous final climb, the escapees still had a lead of around four minutes but Nairo Quintana's Movistar team were setting the pace in the peloton in an attempt to push their leader into GC contention.
Just before the catch was made, Arango made his move. From the peloton, Diaz and Quintana attacked, along with Eduardo Sepúlveda (Bretagne- Séché).
Just as the climb reached its summit, Diaz, using every last drop of energy, attacked once more, catching Arango and powering to the line to take the stage win and extend his lead at the top of the general classification.
"I felt very strong on the climb even though the speed was really high at the bottom," Diaz said.
"Nairo attacked twice. The second time, I knew that it was time to act.
"I don’t think a one-minute lead is enough," Diaz said.
"The time trial could make a big difference and you could very easily lose a minute on the last mountain stage if you have a bad day, so it’s definitely not over."
Stage 5 is a 17.4 kilometre individual time trial around San Luis.