Cycling-Contador's hopes dented, Sagan takes lead with stage win

* Contador suffers second crash in two days, loses time * Sagan pips Alaphilippe to snatch yellow jersey * Porte loses ground after puncture (Adds Contador quotes) By Julien Pretot CHERBOURG, France, July 3 (Reuters) - Alberto Contador's Tour de France chances took another knock on Sunday as the Spaniard lost time to the big favourites, 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. "The team worked well, it's great to wear the yellow jersey. I'm a bit sad for Alberto but he is alright. He is strong," said Sagan. Contador, who fell off his bike 60 kilometres 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). Australian Porte, another podium contender, suffered a puncture in the finale and lost 1:45. "I lost more time than I had hoped to lose. I suffered another crash, I hit the handlebars and I was hurt on the other side from yesterday. I must stay calm, not lose morale, I'm still standing but I have been really touched," the 33-year-old Contador said. "The Tour has really started on the wrong footing. I'm not happy at all. It's cycling. I must see if I can make up some time in the Pyrenees and the Alps, see what I can do. I'm physically hampered. I cannot pedal as I would like to as a result of crashes. "The important thing is to keep my morale, not fall apart, which is sometimes complicated. Both legs are very touched." FROOME AND QUINTANA IN SAFE PLACE Belgian Jasper Stuyven thought he had the stage in the bag after attacking his breakaway companions with 8.5km left but he was caught 450 metres from the line as the stage favourites launched their effort. Contador, Tour winner in 2007 and 2009, hit the deck again on a slippery road as part of a pile-up also involving Frenchman Warren Barguil, German Tony Martin and Spain's Joaquim Rodriguez. After changing his bike, Contador was brought back into the bunch by several team mates but he could not follow the best. Another favourite, France's Thibaut Pinot (FDJ), lost 11 seconds. Sagan leads Alaphilippe overall by eight seconds and Valverde, who finished third overall last year, by 10. Defending champion Chris Froome (Team Sky) and last year's runner-up Nairo Quintana (Movistar) are 14 seconds off the pace in fifth and seventh positions respectively. Sagan, the first rider to swap the rainbow jersey for the yellow jersey since Cadel Evans in 2010, looks set to retain his lead in Monday's third stage, a mostly flat ride over 223.5km from Granville to Angers. Asked how long he hoped he could retain the yellow jersey, Sagan said: "I don't care. If I don't have the yellow I'll have the green (jersey for the points classification) and if I don't have the green I'll have the rainbow jersey." (Editing by Ed Osmond and Clare Fallon)