By Alasdair Fotheringham
TARAZONA, Spain (Reuters) - Vincenzo Nibali of Italy overcame a wasp sting to regain the overall lead the Tour of Spain following the individual time trial on Wednesday.
Astana's Nibali completed the 38.8-kilometre rolling course in fourth place, one minute 25 seconds behind stage winner Fabian Cancellara of Switzerland, with Tony Martin of Germany second and Italy's Domenico Pozzovivo third.
As the race reaches its half-way point, Nibali leads overall by 33 seconds from Ireland's Nicolas Roche with Spain's Alejandro Valverde third.
Overnight leader Chris Horner of the United States slipped to fourth after finishing 20th in the time trial.
Stung by a wasp during a training session on Tuesday, Nibali, who won the Giro d'Italia in May and the 2010 Tour of Spain , said had no way of knowing how much the sting would affect his ride.
"I'm not sure, When I woke up this morning I felt terrible and little by little it's getting better now," Nibali told reporters, wearing dark glasses to protect his red and swollen eyes.
"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."
He named Spaniards Valverde and Joaquim Rodriguez, second and third in the 2012 Vuelta, as his most dangerous rivals.
Horner lost 90 seconds to Nibali, around 30 seconds more than he was hoping for.
"I figured if I lost around a minute on Nibali, it'd be ok," he said before describing his own insect problem when a bee got into his mouth at the beginning 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.
Former World and Olympic time trial champion Cancellara said his victory on a difficult course represented solid progress towards his end-of-season targets at the world championships.
"Before the Vuelta, I had thought this course wouldn't suit me, but when I went out there and looked at it, I thought I had more of a chance and I just focused on doing my race," Cancellara told reporters.
"I really did my homework."
The winner of two major Classics, Paris-Roubaix and the Tour of Flanders, this year, Cancellara would not be drawn on whether he would target the world championships time trial, which he has won four times or the road race.
"For now, I'm just building up my form, I'm getting there and that's what counts. Closer to the time, we'll decide on which race I'll do."
The Tour of Spain finishes on September 15 in Madrid.
(Editing by Ed Osmond)