Team Sky's Vasil Kiryienka claimed a magnificent solo victory on stage 18 of the Vuelta a Espana as Chris Horner cut Vincenzo Nibali's overall lead to just three seconds after dropping the Italian on the day's final climb.
Kiryienka had been part of a 15-man breakaway but struck out on his own with 45km to go and then produced a formidable show of strength to hold on for a 28-second triumph over second-placed Chris Anker Sorensen (Saxo-Tinkoff).
Horner (RadioShack-Leopard) finished sixth but was the stage's big winner in the general classification after comprehensively out-climbing all of his rivals on the category-one ascent to the summit finish on Pena Cabarga.
He entered the final 1km together with Nibali (Astana) and Joaquim Rodriguez (Katusha), but when the gradient ramped up to a punishing 20 per cent, he rode away from both of them and crossed the line 25 seconds ahead of a visibly wilting Nibali.
Horner closes gap
It is the second time that Horner has dropped the red jersey-wearer in successive summit finishes and, with two more mountainous stages to come in the next two days, the 41-year-old now appears favourite for overall victory.
Stage 18 started in Burgos and took the riders on a attritional, 186.5km route containing five categorised climbs. The breakaway group escaped from the peloton early and steadily built up a lead of over ten minutes, but as the barrage of ascents took its toll, the gap fell to under five minutes as the riders entered the final 50km.
Sensing a potential catch, Kiryienka upped his pace over the day's fourth climb, the category-two Alto de Caracol, and although Adam Hansen (Lotto-Belisol) and Simon Clarke (Orica-GreenEDGE) tried to follow, neither could keep up and the Belarusian soon led solo.
He swiftly set about re-opening the lead to over six and a half minutes and simultaneously managed to keep a three-man chase group consisting of Sorensen, Angel Vicioso (Katusha) and Egoi Martinez (Euskaltel-Euskadi) at arm's length.
Kiryienka too strong
That trio later became eight when other members of the original breakaway bridged over, but they were more than 1min 40sec down on Kiryienka when he started up the 6km final climb and although Sorensen launched a strong counter-attack, his Belarusian rival was in menacing form and could not be caught.
"It was an incredible feeling when I wrapped up the victory," Kiryienka told teamsky.com. "Once the road ramped up it was a matter of riding just below threshold and then judging my efforts over the steeper sections of the climb."
Back down the road, the peloton was severely thinned down on the lower slopes of the Pena Cabarga climb and then Rodriguez blew it apart further when he and two team-mates attacked 1.5km out.
Their move successfully dropped Alejandro Valverde (Movistar), but Horner and Nibali stayed calm and soon reeled Rodriguez back in. However, Horner still had a card to play and Nibali's woes were compounded when Valverde recovered and overtook him in the final few metres.
Stage 18 result
1 Vasil Kiryienka (Blr) Team Sky, 4:46:48
2 Chris Anker Sorensen (Den) Saxo-Tinkoff, +28
3 Adam Hansen (Aus) Lotto-Belisol, +1:18
4 Martin Kohler (Sui) BMC, +1:34
5 Egoi Martinez (Spa) Euskaltel-Euskadi, +1:42
6 Chris Horner (USA) RadioShack-Leopard, +1:53
7 Amets Txurruka (Spa) Caja Rural, +2:02
8 Joaquim Rodriguez (Spa) Katusha, +2:13
9 Alejandro Valverde (Spa) Movistar, +2:14
10 Vincenzo Nibali (Spa) Astana, +2:18
1 Vincenzo Nibali (Spa) Astana, 73:39:35
2 Chris Horner (USA) RadioShack-Leopard, +3
3 Alejandro Valverde (Spa) Movistar, +1:10
4 Joaquim Rodriguez (Spa) Katusha, +2:24
5 Nicolas Roche (Irl) Saxo-Tinkoff, +3:43
6 Domenico Pozzovivo (Ita) Ag2r-La Mondiale, +5:44
7 Thibaut Pinot (Fra) FDJ, +6:14
8 Leopold Konig (Cze) NetApp-Endura, +6:35
9 Samuel Sanchez (Spa) Euskaltel-Euskadi, +7:51
10 Tanel Kangert (Esa) Astana, +11:10
- Green (points classification): Alejandro Valverde (Movistar)
- Blue polka dot (mountains classification): Nicolas Edet (Cofidis)