Madrid - Italian Vincenzo Nibali has clung on to his narrow lead of the Tour of Spain after a gruelling 18th stage on Thursday.
Sky's Belarusian rider Vasil Kiryienka won the stage after breaking away at the end of the 186.5km ride from Burgos to Pena Cabarga that featured five categorised climbs, including a tricky final ascent.
Kiriyenka's breakaway to the summit of Pena Cabarga almost cost Nibali his lead atop the general classification, now cut to just three seconds.
The Sicilian, who rides for Astana, couldn't respond to a push by the Katusha team in the final ascent, and then the attack by RadioShack's 41-year-old American rider Chris Horner, who was sixth across the finish line.
Nibali, who finished 10th 25sec off Horner, also gave away time to Spaniards Alejandro Valverde (Movistar), now third in the overall standings at 1:10, and Joaquim Rodriguez (Katusha), fourth at 2:24.
"Horner is very strong, it's incredible what he's doing at almost 42 years of age," Nibali told Spanish television at the end of the race.
"Horner showed he's one of the great pretenders for this Vuelta."
Horner said: "I can't stress on three seconds right now.
"I made up a lot of time today and the gap is smaller; that's what is important to me.
"Three seconds. I guess it won't matter either way if I get dropped on one of the next two stages.
"We'll have to see how things go.
"The team is fantastic, I just can't thank them enough."
Kiryienka, who bowed out of the Tour de France in July after missing the time cut on stage nine in the Pyrenees, was one of an initial 15-strong group to break away from the main peloton, and attacked in Alto del Caracol, 45km from the finish.
The 32-year-old arrived at the foot of the Pena Cabarga with 1:30 on his rivals and managed his ride-in to perfection.
"I woke up this morning thinking it could be a stage for me," said Kiryienka.
"I chanced my arm and there's the result."
Friday's 19th stage sees the riders tackle 181km with the finish again at altitude, demanding a first-category climb to Alto del Naranco before tackling the infamous Alto de l'Angliru on Saturday's stage.
"Saturday's climb is the better day for me, but when you are going against the best guys in the world, you have to pay attention on every stage," said Horner.
"Tomorrow could be a game of tactics.
"I thought I could take the jersey today but I was three seconds off.
"I just need to keep my form for another few days to get the red jersey and take it to Madrid."
Leading results from the 18th stage of the Tour of Spain, a 186.5km ride from Burgos to Pena Cabarga on Thursday:
1. Vasil Kiryienka (BLR/SKY) 4h 46min 48sec
2. Chris Anker Sorensen (DEN/SAX) at 0:28.
3. Adam Hansen (AUS/LTB) 1:18.
4. Martin Kohler (SUI/BMC) 1:34.
5. Egoi Martinez (ESP/EUS) 1:42.
6. Chris Horner (USA/RSH) 1:53.
7. Amets Txurruka (ESP/CJR) 2:02.
8. Joaquim Rodriguez (ESP/KAT) 2:13.
9. Alejandro Valverde (ESP/MOV) 2:13.
10. Vincenzo Nibali (ITA/AST) 2:18.
11. Nicolas Roche (IRL/SAX) 2:18.
12. Thibaut Pinot (FRA/FDJ) 2:24.
13. Michele Scarponi (ITA/LAM) 2:24.
14. Daniel Moreno (ESP/KAT) 2:31.
15. Samuel Sanchez (ESP/EUS) 2:36.
16. Leopold Koenig (CZE/APP) 2:36.
17. Tanel Kangert (EST/AST) 2:36.
18. Diego Ulissi (ITA/LAM) 2:49.
19. Igor Anton (ESP/EUS) 2:49.
20. Reinardt Janse Van Rensburg (RSA/ARG) 2:53.
1. Vincenzo Nibali (ITA/AST) 73h39min 35sec
2. Chris Horner (USA/RSH) at 0:03.
3. Alejandro Valverde (ESP/MOV) 1:09.
4. Joaquim Rodriguez (ESP/KAT) 2:24.
5. Nicolas Roche (IRL/SAX) 3:43.
6. Domenico Pozzovivo (ITA/ALM) 5:44.
7. Thibaut Pinot (FRA/FDJ) 6:14.
8. Leopold Koenig (CZE/APP) 6:35.
9. Samuel Sanchez (ESP/EUS) 7:51.
10. Tanel Kangert (EST/AST) 11:10.
11. Daniel Moreno (ESP/KAT) 11:15.
12. Michele Scarponi (ITA/LAM) 12:14.
13. Jose Herrada (ESP/MOV) 12:30.
14. David Arroyo (ESP/CJR) 13:48.
15. Igor Anton (ESP/EUS) 16:46.
16. Dominik Nerz (GER/BMC) 18:28.
17. Robert Kiserlovski (CRO/RSH) 19:37.
18. Chris Anker Sorensen (DEN/SAX) 20:21.
19. Eros Capecchi (ITA/MOV) 23:26.
20. Andre Cardoso (POR/CJR) 23:55.