The 101km stage from Saint-Girons to Foix, which included three Category 1 climbs packed into its short distance, was the scene of the most animated racing of the Tour to date.
Sunweb's Warren Barguil punched his way to a French win on Bastille Day but it was the General Classification battle which intrigued, with Aru riding defensively as his position came under threat.
"We expected that the stage will be very hard and exhausting," Aru said. "There were a lot of attacks, especially, on the last downhill. But, I tried to keep my concentration and act with a cool head and without too much stress."
That cool head worked in his favour and he ended the day as he started, leading Chris Froome (Sky) by six seconds and Romain Bardet (AG2R) by 25.
"It worked well and it is another day in the yellow jersey for me. I try to take my leaderships calmly," he said. "There is a long way to Paris, we have to pass through many tough stages. Tomorrow is another day and another stage, which will request all our forces. So, we will keep on fighting.
The list of riders determined to crack the Sardinian included Alberto Contador (Trek-Segafredo), Mikel Landa (Sky), Nairo Quintana (Movistar) while Froome and Bardet were content to mark the race leader.
However, Aru's task became just that little bit harder with injured Astana team-mate Jakob Fuglsang forced out after struggling gamely with a fractured wrist.
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The Dane arrived at the Tour as Astana's second option after winning the Critérium du Dauphiné and would have been a key lieutenant when the race heads to the Alps and Aru will likely miss his firepower.
"I did all I could, but all left part of my body just did not want to work. I had no power to stay in the group," Fuglsang said.
"Right from the start the speed of the peloton was very high, so I had to continue following my own rhythm. But before the last climb I’ve realised, it is just too much for me, I had to give up.
"It is not easy at all to leave the Tour de France and my team, but there is nothing to do. The main goal for me now is to get a full recovery."
There will be some respite for Aru on Stage 14 and 15 before the rest day and an appointment with the Alps and potential destiny as a Tour winner.
