Mountain king Arredondo takes Giro 18th stage
Overall leader, Colombian cyclist Nairo Quintana frees some balloons before the start of the 18th stage of the 97th Giro d'Italia cycling race, Tour of Italy, from Belluno to Rifugio Panarotta, on May 29, 2014 - by Luk Benies
Trek's Arredondo broke clear of an escape group in the final 4km and held off another compatriot Fabio Duarte to take the victory by 17sec.
Irishman Philip Deignan of Team Sky took third on the stage, 37sec back at the end of the 171km stage from Belluno to Rif. Panarotta.
Australian 2011 Tour de France winner Cadel Evans was the big loser as he was dropped by the group of favourites and lost his podium place.
The 37-year-old BMC rider dropped to ninth overall from third at the beginning of the day.
Quintana, who took the leader's maglia rosa (pink jersey) by winning Tuesday's 16th stage, leads another Colombian, Rigoberto Uran, by 1min 41sec with Frenchman Pierre Roland up to third overall at 3min 29sec.
Arredondo soloed to the biggest win of his life in a thrilling finish on the final climb in which the lead changed hands several times.
After Belgian Thomas De Gendt and Italian Franco Pellizotti had both tried their luck, Arredondo finally made a solo break stick.
Duarte, who had covered an earlier dig from Arredondo 6km out, tried to respond but this time could not bridge the gap.
Behind the breakaway riders, the battle was on for podium places as Movistar's Quintana expertly marshalled any danger to his overall lead.
Evans was the first to crack giving Roland, whose attacks thinned out the favourites' group, the chance to snatch a podium spot.
However, he has two riders just two seconds back after Italian Fabio Aru of Astana pulled back a handful of second on the Europcar rider.
Aru is fourth on the same time as fifth-placed Rafal Majka with Italian Domenico Pozzovivo just 23sec behind Roland in sixth.