Alberto Contador extended his overall Giro d'Italia lead to over five minutes after a bold attack in the 18th stage, a 170km trek from Melide, Switzerland, to Verbania won by former world champion Philippe Gilbert on Thursday.
The Spaniard, looking to become the first man since the late Marco Pantani in 1998 to achieve the Giro/Tour de France double,  attacked in the punishing climb to Monte Ologno, gaining over a minute over his main rivals.
He got help from Cannondale-Garmin riders Ryder Hesjedal, a former Giro champion, and Davide Villella, as the trio continued to pull clear in the descent to Verbania.
Belgian Gilbert (BMC) jumped away from the breakaway group and soloed to his second stage win of this year's Giro.
According to provisional results, Tinkoff Saxo's Contador, who crossed the line 1:13 ahead of his main rivals, leads second-placed and compatriot Mikel Landa (Astana) by 5:15 and Italian Fabio Aru (Astana) by 6:05.
Friday's 19th stage is a 236km ride featuring three categorised climbs and ending uphill in Cervinia.
The Giro ends in Milan on Sunday.