Chris Froome was penalised 20 seconds for taking an illegal feed inside the final five kilometres on today's double ascent of the Alpe d'Huez, but still increased his overall lead in the 100th Tour de France.

As Christophe Riblon raced to victory ahead to become France's first stage winner this year, Froome showed his first signs of distress all Tour when he waved for help just after the 5km post.

Richie Porte dropped back to the team car to get an energy bar for the yellow jersey holder, but race commissaires docked the time from Froome.

Nevertheless, he still increased his lead over Alberto Contador to five minutes 11 seconds after finishing in seventh place, almost a minute ahead of the Spaniard on the road.

Dan Martin finished back in 76th place, 25:10 off the lead, while Nicolas Roche finished 131st, 30:03 behind Riblon.

Overall, Martin drops to 19th place in the general classification, 34:22 off the lead, while Roche is placed 42nd, 1:13:50 behind current leader Froome.

"That's one of those things that comes with the race," Froome said of the penalty. "I really felt that I needed those sugars at the end. If it comes with a 20-second penalty I have to accept that."

Porte was also docked 20 seconds for his role in the incident.

Richie Porte congratulates team-mate Chris Froome as he crosses the line

Froome has looked imperious on the climbs during this Tour, winning on the toughest mountain stages in Ax 3 Domaines and on Mont Ventoux.

But today he clearly struggled on the second of the two ascents.

Although he had kicked clear of Contador with around 11km to go, Nairo Quintana stayed with him and the Colombian eventually finished more than a minute clear, putting him third overall five minutes 32 seconds back.

Froome had finished seventh alongside Porte in sixth, and - regardless of any penalty - he will be happy to see his overall lead increased on such a dangerous stage.

With the forecast thunderstorms staying away, Contador had attacked Froome on the feared descent of the Col de Sarenne which linked the two ascents of the Alpe.

Throwing caution to the wind, he and team-mate Roman Kreuziger pulled 20 seconds clear, but could not stretch it any further and instead sat up to be caught before the second climb.

No sooner had he been caught than he had dropped back for a bike change, although he was back with Froome on the early part of the climb.

Christophe Riblon (r) and Tejay van Garderen (c) pass cycling ultra El Diablo

Movistar were leading the little pack in a bid to put Quintana in a winning position but it was Froome who kicked a little over 11 kilometres from the summit.

Quintana followed but Contador could not and quickly began to fall away.

Up ahead, Tejay Van Garderen, Christophe Riblon and Moreno Moser had begun their second ascent together - the last remnants of a nine-man breakaway - but the American Van Garderen soon kicked clear, building a lead of 40 seconds.

However, Riblon began to close in before the five kilometre mark, before Froome's late drama at the same point.