Giovanni Visconti claimed his first stage win on the Giro d'Italia after digging deep to conquer the gruelling conditions, with much of the high mountains covered in unseasonal snow that continue to blight this year's race.
The Movistar rider was part of an initial six-man breakaway group that pulled clear of the peloton with 82 kilometres (50 miles) remaining of the 145km (90-mile) stage from Cesana Torines.
Visconti asserted his dominance as further snow arrived to add more danger to an already gruelling Alpine trek, the Italian coming home in 4hr 40min 52sec, 42sec clear of Carlos Betancur (Ag2R-La Mondiale).
Vincenzo Nibali, the Astana team's overall race leader, was 12sec further back, alongside his nearest challenger for the pink jersey, Cadel Evans (BMC).
Nibali's lead in the general classification remains at 86sec over Australia's Evans.
Team Sky's Rigoberto Uran crossed the line in 10th place alongside Nibali and Evans to maintain his position of third in the overall standings, but he is 2min 46sec back with just six stages remaining.
"I wanted to squeeze out some more time on my rivals and tried accelerating away from them at the end but, even if that didn't work, I'm still very pleased with how things stand overall," Nibali said.
"Today was a good day, I've got a good advantage on my rivals."
With the stage dedicated to the former Italian champion Marco Pantani, who forged his 1998 Tour de France victory with an attack on the Galibier, Nibali said he had wanted to put on a good performance "to honour one of the greatest riders".
The 28-year-old Sicilian, who won the Vuelta, the Tour of Spain, in 2010, said: "It was only right to go for it today, even if the cold didn't help matters because it made it really hard to go on the attack. The weather conditions really influenced the way the stage played out today."
Yesterday's stage only went ahead after race organisers and local officials agreed to shorten the distance by 4km, thereby missing the worst of the sub-zero conditions expected at the very summit of the fearsome Col du Galibier.
After the rain, snow and fog that blighted Saturday's 14th stage, the riders appeared to agree to neutralise the day's first climb on the Col du Mont Cenis, with the first serious breakaway not coming until that summit was cleared.
Visconti was in the mix when the break came, with still more than half the stage to race, pulling away with Stefano Pirazzi, Francesco Bongiorno, Robinson Chalapud, Pieter Weening and Matteo Rabottini.
Visconti took his lead out to almost a minute as he tackled the curtailed ascent of the Galibier. The snow started to fall with 3km remaining, but even that could not put Visconti off his rhythm as he came home for a famous victory ahead of today's rest day that will be welcomed by all the riders.
Overall standings after stage 15
1 V Nibali (It) Astana, 62:02:34 2 C Evans (Aus) BMC +1:26"
3 R Uran (Col) Sky +2:46"
4 M Santambrogio (It) Vini +2:47"
5 M Scarponi (It) Lampre +3:53"
6 P Niemiec (Pol) Lampre +4:35"
7 C Betancur (Col) Alm +5:15"
8 R Majka (Pol) TST +5:20" 9 D Pozzovivo (Ita) Alm +5:57"
10 M Belkov (Rus) +44:51"