Richie Porte was the big loser in today's first big mountain stage of the Tour de France as the Australian slipped from 2nd to 16th in the overall standings. While his Sky team now promises to go on the attack, Porte himself thinks the heat played a key role in his collapse.

Richie Porte endured a difficult day on stage 13 of the Tour de France and dropped out of the top 10 in the searing heat.

The Tasmanian headed into the key mountainous test in second overall but began to slip back on the hors-categorie climb up to Chamrousse.

Paced by team-mates Mikel Nieve and Geraint Thomas the trio crossed the line eight minutes and 48 seconds back, moving Porte back to 16th overall after a difficult stage

The day belonged to Vincenzo Nibali who claimed his third stage win of the race and extended his overall lead to 3:37 over Alejandro Valverde (Movistar) in a great show of strength.

The Astana rider attacked his main rivals with 6.7km to go and rode clear, eventually bridging across to Rafal Majka (Tinkoff-Saxo) and Leopold Konig (NetApp-Endura) before coming home 10 and 11 seconds ahead of the duo respectively.

As riders scrambled to retain contact small groups were strewn across the Alpine climb, with Valverde and Thibaut Pinot (FDJ.fr) the next men home, while Romain Bardet (Ag2r-La Mondiale) did enough to edge onto the final step of the podium.

“I don’t think I dealt with the heat very well,” admitted Porte back at the team bus. “It’s one of those things. It’s a massive shame but we’ll see what happens tomorrow.

“I feel more for my team-mates who have been brilliant for me every day. If it happens to me it can happen to other guys too. We’ll just keep on pushing.”

Team Principal Dave Brailsford added: "It was a difficult day but we’ll keep on fighting.

"Obviously it was a blow losing Chris (Froome) when you come here to win the race. Certainly, seeing how Nibali is going it would have been an interesting race. And then we recalibrated to our plan B as it were and now we have to recalibrate again.

"You've got to take account of the situation, not get too downbeat, there's a lot of racing to go. Let's see how the next few days go. We have to try to animate the race as much as we can and go from there.

"Richie's disappointed and when you're disappointed it's not the time to start analysing. On the last climb, It was just a question of minimising his losses to be honest. 

"We’ve had some terrific performances in the last couple of years at the Tour de France. We’d have liked to see that happen again but every now and again in sport you get dealt a tough blow. Today is one of those for us but we’ll come back and keep on racing to the end in Paris."