Italy's Daniele Ratto defied torrential rain and plummeting temperatures to claim a magnificent solo victory on stage 14 of the Vuelta a Espana as Vincenzo Nibali extended his overall lead.
Ratto (Cannondale) broke away with four other riders after just 3km of a day marred by abysmal weather and later forged clear on his own for the biggest win of his career.
Nibali (Astana) and Chris Horner (RadioShack-Leopard) finished almost four minutes later in second and third respectively after dropping all of their rivals for overall victory on the climb to the summit finish on the Collada de la Gallina.
Joaquim Rodriguez (Katusha) limited his losses to the pair to 16 seconds, but Alejandro Valverde (Movistar) shipped almost a minute after falling behind earlier in the stage as he struggled in the severe cold.
Ireland's Nicolas Roche (Saxo-Tinkoff) fared even worse, losing three and a half minutes after suffering badly from a combination of the conditions and the steep final climb.
The weather was so bad that Ivan Basso (Cannondale), who had been seventh in the general classification, and breakaway rider Luis Leon Sanchez (Belkin) were both forced to abandon the race through hypothermia. They were among 14 riders who failed to finish the stage.
The day's outcome means Nibali strengths his grip on the red jersey from 31 seconds to 50 seconds, with Horner moving back up to second place and Roche dropping to sixth.
The 155.7km stage had promised to be one of the marquee days of the Vuelta, with an ascent of the especial-category Port de Envalira - the race's highest point at 2,410m - being followed by the Gallina, which was first of three consecutive Pyrenean summit finishes.
A high-pedigree, five-man breakaway moved clear just after the start flag and built up a sizeable lead, but they were reduced to just Ratto, Sanchez and world champion Philippe Gilbert (BMC) on the lower slopes of the 26.7km climb of the huge Envalira.
The trio stretched their lead to over 12 and a half minutes as they crested the summit, but then Ratto moved into sole lead by descending down the other side at a breakneck pace, despite the rain-soaked road surface.
Ratto holds on
He then safely navigated two smaller climbs and after reaching the foot of the 7.2km Gallina ascent with an 8min 45sec lead, his victory was effectively secured.
Behind, Horner's team-mate Robert Kiserlovski set a fierce pace on the front of a severely reduced peloton on the lower slopes of the climb and Roche was the first to crack under the strain, with Rodriguez, Domenico Pozzovivo (Ag2r-La Mondiale) and Thibaut Pinot (FDJ) all later following in him in falling away.
After Kiserlovski pulled aside, only Nibali and Horner remained out front, and having allowed Horner to lead him to the final 200m, Nibali darted in front at the death to ensure he took the best of the remaining bonus seconds.
Rodriguez recovered well to take fourth, while Valverde produced a superb display on the final climb to save his third place in the GC.
Stage 14 result
1 Daniele Ratto (Ita) Cannondale, 4:24:00
2 Vincenzo Nibali (Ita) Astana, +3:53
3 Chris Horner (USA) RadioShack-Leopard, +3:55
4 Joaquim Rodriguez (Spa) Katusha, +4:11
5 Samuel Sanchez (Spa) Euskaltel-Euskadi, +4:19
6 Alejandro Valverde (Spa) Movistar, +4:43
7 Thibaut Pinot (Fra) FDJ, +4:46
8 Domenico Pozzovivo (Ita) Ag2r-La Mondiale, same time
9 Mikel Landa (Spa) Euskaltel-Euskadi, +5:17
10 Leopold Konig (Cze) NetApp-Endura, +5:21
20 Nicolas Roche (Ire) Saxo-Tinkoff, +7:22
1 Vincenzo Nibali (Ita) Astana, 53:56:49
2 Chris Horner (USA) RadioShack-Leopard, +50sec
3 Alejandro Valverde (Spa) Movistar, +1:42
4 Joaquim Rodriguez (Spa) Katusha, +2:57
5 Domenico Pozzovivo (Ita) Ag2r-La Mondiale, +3:43
6 Nicolas Roche (Ire) Saxo-Tinkoff, +4:08
7 Thibaut Pinot (Fra) FDJ, +4:34
8 Leopold Konig (Cze) NetApp-Endura, +5:42
9 Daniel Moreno (Spa) Katusha, +6:28
10 Tanel Kangert (Est) Astana, +6:45
- Green (points classification): Alejandro Valverde (Spa) Movistar
- Blue polka dot (mountains classification): Daniele Ratto (Ita) Cannondale