Sagan is hoping to claim a record-extending eighth green jersey but he has been far from his best this season.
The defending champion came seventh, one second behind stage winner Michael Matthews of Australia as Aru, who started the day with the yellow jersey on his shoulders, lost 25 seconds to the Briton in the final effort, a 600-metre climb at an average gradient of 9.6 per cent.
The seventh stage of the Tour de France burst into life at the finish on Friday as Marcel Kittel claimed his third victory in this year's edition, pipping Edvald Boasson Hagen to the line in the final sprint.
Hold your breath as Rediff.com brings to you some of the picturesque places that the cyclists race through at the Tour.
Geraint Thomas tightened Team Sky's grip on the Tour de France when he handed the British outfit their sixth title in seven years on Sunday and there is no sign that their domination will end anytime soon.