Samuel Sanchez, the Spanish climbing specialist, won yesterday's 12th stage of the Tour de France when he overtook a group of breakaway riders in the final climb and held on.
Thomas Voeckler of France retained the overall lead as the race entered the high mountains for the first time.
"It's incredible," Sanchez said of his first Tour stage win, after finishing fourth overall last year.
After a string of setbacks earlier in the race Alberto Contador, the defending champion, struggled up the main climb and lost crucial seconds to other pre-race favourites for overall victory.
The 211-kilometre trek from Cugnaux to the Luz-Ardiden ski station featured three tough climbs in the Pyrenees - including two that are among the hardest in professional cycling.
After Sanchez and the Belgian rider Jelle Vanendert overtook the breakaway group on the final climb,the Spaniard won their two-man sprint in the last several hundred metres. Vanendert crossed seven seconds later.
After leading a string of attacks on the other pre-race favourites, Frank Schleck of Luxembourg surged away and finished third - 10 seconds back - to vault into second place overall. Italy's Ivan Basso was fourth, Cadel Evans of Australia was fifth, and Schleck's younger brother Andy was sixth. Contador came eighth, 43 seconds back.
Voeckler gave the home crowd a delight for France's national Bastille Day holiday, clinging to the yellow jersey that he had expected to lose in the punishing climbs.
"I'm glad I was wrong," Voeckler said. "It clearly wasn't expected. Keeping the jersey was far from expected as the stage started today."
"You have to believe that the yellow jersey gives you a bit of added inspiration on the Bastille Day."
Earlier in the race, Voeckler and the German Andreas Kloden were among a small group of riders who fell victim to a pile-up just after the chasing peloton had crested the first of three major climbs, La Hourquette d'Ancizan, 141.5km into the stage.
Voeckler skidded before tumbling into a car parked at the side of the road after breaking to avoid crashing harder.
In his wake Kloden, who is competing despite suffering from a back injury sustained in a heavy crash on stage nine on Sunday, came down much harder.
Kloden, a former podium finisher got back on his bike to continue, apparently suffering from grazes and cuts to his right shoulder and elbow.
His RadioShack team are already reeling following the retirements of Chris Horner and Janez Brajkovic, two key riders for the crucial mountain stages.
Six minutes earlier, Geraint Thomas of Wales, who was part of an early six-man breakaway, provided drama when he almost crashed twice within 500 metres.
Shortly after cresting the summit the Team Sky rider braked hard as he came around a right-hand bend and, as he headed towards the grass and a possible drop over the edge, he came off his bike.
Thomas got back on but barely 500 metres further on he rode into the grass verge again after failing to negotiate a left-hand bend.
Thomas was unaware that there was a €5,000 (Dh26,000) prize for being the first rider over the 2011 Tour's first hors categorie (beyond category) climb, the Col du Tourmalet. The Welshman was beaten to the summit of the 17.1km fabled Pyrenean peak by breakaway companion Jeremy Roy.
Overall, Voeckler leads Frank Schleck by 1min, 49 secs, and Evans trails third, 2:06 back. Contador is seventh overall, four minutes behind.
"I was a bit careful," the three-time Tour champion said. "I saw the Schlecks were discussing together and that they were going to play their cards. Frank was the stronger - and both of them attacked."
"But I'm nevertheless happy with this first mountain stage," Contador said. "Each day, I feel better ... I still don't have my best legs. I'm not riding with the same rhythm, but it's encouraging."