Tour de France: Sweet and sour for leader Chris Froome

Briton handed 20-second penalty for "illegal feeding".

The peloton negotiates a tight bend on Stage 18 of the Tour de France from Gap to l’Alpe d’Huez on Friday.

L'ALPE D'HUEZ, France // Chris Froome showed rare signs of weakness on Thursday despite extending his overall lead on the Tour de France in the 18th stage, won after two epic ascents of l'Alpe d'Huez by France's Christophe Riblon.

The Briton cracked with less than 5km remaining on the second trip up the mountain's 21 hairpin bends, but sent teammate Richie Porte to fetch some food and the Australian nursed Froome to the finish 3:18 behind Riblon, who became the first Frenchman to win a stage in this year's race.

"I was running low on sugars," Froome said after the stage. "I am thankful to have Richie with me he did a super, super job."

Froome and Porte were each given a 20-second penalty for "illegal feeding" as organisers said the riders were not allowed to take food or liquid from the team car during the final 6km of the stage.

However, Froome still leads Alberto Contador, the 2007 and 2009 Tour champion, by 5:11, after the Spaniard struggled to keep the pace in the final ascent following a bold-but-brief attack on the treacherous descent from the Col de Sarenne.

Contador, who was 11th on the stage, 57 seconds behind Froome, heads Colombian Nairo Quintana by 21 seconds overall after the Movistar climber, targeting a podium finish in Paris, took fourth place on the stage, more than two minutes off the pace.

"Throughout the entire race, we've said that we wanted the overall win and we were not afraid of risking it all to get it and so we did today," said Contador's team director Fabrizio Guidi.

"But the legs just weren't good enough to finish it off. We can be disappointed and everyone's a lot wiser after the stage, but if you never try, you never win.

"We're still competing for the top positions and there are still two demanding stages to go. Now, it's time to keep focused, remain calm, recover and try again tomorrow."

Meanwhile, Team Sky principal Dave Brailsford confirmed he had written to the World Anti-Doping Agency to offer them details of Froome's performances in a bid to end the climate of suspicion surrounding the rider.

Froome's string of stunning performances have aroused suspicion from fans and journalists, who remain sceptical in the wake of the Lance Armstrong scandal.

"We have been in contact with WADA and the UK Anti-Doping agency and things are progressing," Brailsford said.

"We are trying to react to a situation, trying to think creatively about a situation.

"Nobody asked me to do this. I suggested it would be a good idea to contact them. They didn't contact me."

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