By Julien Pretot CHERBOURG, France (Reuters) - Alberto Contador's Tour de France chances took another knock on Sunday as the Spaniard lost time to the big favorites, crashing for the second time in as many days during the second stage won by his team mate and world champion Peter Sagan. Slovak Sagan perfectly timed his effort in the final climb to pip France's Julian Alaphilippe (Etixx-Quick Step) and Spain's Alejandro Valverde (Movistar) and take the overall leader's yellow jersey from Mark Cavendish. Contador, who fell off his bike 60 kilometers into the 183-km ride from Saint Lo, crossed the finish line 48 seconds behind Sagan and the other top guns with the exception of Australian Richie Porte (BMC). More...