Schleck had accelerated less than 4 kilometers from the top of the big climb of the day, the Port de Bales, but almost immediately lost his chain, forcing him to stop on the side of the road and wait for assistance.
He then had to force his way back through the field as he attempted to catch up with Contador and the other leaders in the overall competition, but was unable to make up enough time. Contador now holds the yellow jersey by eight seconds from Schleck.
French champion Thomas Voeckler won the day's stage, the second of the Tour de France's four big stages in the Pyrenees, with a solo ride.
Schleck angrily said that according to cycling etiquette the riders should have waited for him, which was what happened when he crashed during an early stage.
“Today, you know, everybody is in panic, they see already the Eiffel Tower. I would not have taken advantage of the situation,” he said. “It's not up to me ... but for sure these guys don't get the fair play prize today.” Contador said he had not been aware of Schleck's problem until he had gone far past him.
“When I launched the attack I wasn't at all aware of this incident,” he said. “When I knew, it was already too late, we were riding far ahead.” It was the second stage victory for Voeckler after another solo win in Perpignan last year. He also held the yellow jersey for nine days in 2004.
He finished Monday's 187.5-kilometer (116.5-mile) 15th stage from Pamiers to Bagneres-de-Luchon in 4 hours, 44 minutes, 51 seconds, ahead of Alessandro Ballan of Italy and Aitor Perez of Spain.
Tuesday's 16th stage, the third in the Pyrenees, is one of the toughest of all, taking the riders 199.5 kilometers (124 miles) from Bagneres-de-Luchon to Pau. The course goes over the major climbs of the Col de Peyresourde, Col d'Aspin and Col d'Aubisque, but the highlight will be the first of two crossings of the legendary Col du Tourmalet.
