Swiss rider Fabian Cancellara won the 11th stage of the Vuelta a Espana as Italian Vincenzo Nibali overcame a wasp sting to lead the overall race.
RadioShack Leopard's Cancellara held off German Tony Martin to win the 38.8km time trial by 37 seconds.
Astana's Nibali, stung in training on Tuesday, finished fourth to secure a 33-second lead over Nicolas Roche.
2013 Grand Tour winners
- Giro d'Italia:
Vincenzo Nibali (Ita)
- Tour de France:
Chris Froome (GB)
"I felt terrible when I woke up this morning and little by little it's getting better," Nibali, 28, said.
"I'm just going to defend the lead day by day, not thinking too far ahead. There's still five really big mountain stages to come."
Ireland's Roche, riding for Saxo-Tinkoff, finished sixth to move up to second in the general classification with Spaniard Alejandro Valverde of Movistar completing the top three.
RadioShack's American rider Chris Horner, who
led after winning the 10th stage,
dropped to fourth in the race for the red jersey after finishing 20th in the time trial.
The 41-year-old was hampered by a bee flying into his mouth at the start of the stage.
"It was disturbing and scary. I couldn't get it out. I also tried to swallow it. Eventually, I coughed it up," Horner said.
"I figured if I lost around a minute on Nibali, it'd be OK."
Thursday's 12th stage is a 164.2km ride from Maella to Tarragona, which is expected to favour the sprinters.
Result of stage 11
Fabian Cancellara (Switzerland / RadioShack) 51:00
Tony Martin (Germany / Omega Pharma-Quick Step) +37"
Domenico Pozzovivo (Italy / AG2R La Mondiale) +1:24"
Vincenzo Nibali (Italy / Astana) +1:25"
Dario Cataldo (Italy / Sky Procycling) +1:41"
Nicolas Roche (Ireland / Saxo-Tinkoff) +1:48"
Alejandro Valverde (Spain / Movistar) +1:52"
Overall standings after 11 stages
Vincenzo Nibali (Italy / Astana) 41:22:22"
Nicolas Roche (Ireland / Saxo-Tinkoff) +33"
Alejandro Valverde (Spain / Movistar) +46"
Chris Horner (US / RadioShack) +46"
Joaquim Rodriguez (Spain / Katusha) +2:33"
Domenico Pozzovivo (Italy / AG2R La Mondiale) +2:44"