Chris Froome produced one of the great performances of his career, attacking alone on a gravel road up a gruelling climb to win the 19th stage of the Giro d'Italia and claim the overall leader's pink jersey.
The four-time Tour de France champion launched his solo attack up the three-week race's highest climb with 80 kilometres to go and rode clear amid banks of snow above the tree line.
Pedalling furiously, Kenyan-born Froome continuously increased his advantage over two more Alpine ascents to finish three minutes ahead of his closest challenger.
The victory put Froome in position to win his third consecutive Grand Tour and match the achievements of the great Eddy Merckx and Bernard Hinault. There are two stages of the Giro left.
"I don't think I've ever attacked 80 kilometres from the finish, riding on my own and going all the way to the finish," Froome said.
"I knew there was a long way to go but to win this Giro d'Italia I had to do something extraordinary. I couldn't wait for the last climb. I had to do something crazy.
"Colle delle Finestre was the perfect place to do it. Gravel roads remind me of Africa."
Froome leads defending champion Tom Dumoulin of the Netherlands by 40 seconds in the overall standings. Frenchman Thibaut Pinot is third overall, 4:17 behind.
There is one more mountainous stage on Saturday, a 214-kilometre leg from Susa to Cervinia, before Sunday's mostly ceremonial finish in Rome.
Froome had started the day fourth overall, more than three minutes behind previous leader Simon Yates.
Yates fell far behind up the gruelling climb on Colle delle Finestre as Froome launched his audacious attack, and finished nearly 40 minutes behind.
It was Yates' 13th day wearing the pink jersey.
Richard Carapaz of Ecuador crossed second in the stage, exactly three minutes behind, and French challenger Thibaut Pinot finished third, 3:07 back.
Dumoulin came fifth, 3:23 behind Froome.
Froome arrived at the Giro with big hopes but had not really been a threat after crashing in training before the opening time trial, losing time in a split on stage four, and injuring himself again in a second crash four days later.
His only previous highlight in the race was winning Stage 14 up Monte Zoncolan, one of the toughest climbs in Europe.
"It was a very, very tough start for me after the fall," Froome said.
"But I kept up my morale for the finish and I knew that if I did everything right the time to attack would come. That moment came today."
Only two riders have ever won three or more consecutive Grand Tours. Merckx won four straight between 1972 and 1973 and Hinault took three in a row in 1982 and 1983.
However, Froome is racing under the cloud of a potential ban after a urine sample he provided at the Spanish Vuelta in September showed a concentration of the asthma drug salbutamol that was twice the permitted level.
It remains unclear when the International Cycling Union will rule on the case.
Froome denies any wrongdoing.