Team Sunweb’s Barguil won from Colombian Nairo Quintana and the Spanish duo Alberto Contador and Mikel Landa as the break-away held out on the 101 kilometre stage from Saint-Girons to Foix.
Chris Froome crossed the line just ahead of Aru in eighth place but could do nothing to cut into the Italian’s six-second advantage at the top of the general classification.
The top four in the fight for yellow – who started the day separated by just 35 seconds – were all in the same group at the finish, which means that AG2R La Mondiale’s Romain Bardet remains third, 25 seconds back with Colombian Rigoberto Uran in fourth.
But Team Sky did make a major impression on the day as Landa’s place in the break saw him claw back one minute and 48 seconds, moving him up to fifth, 69 seconds back.
“Yesterday was a difficult day for me, but today I felt a lot better and we played a lot with our team,” said Froome. “We had Mikel not a long way back on GC, and maybe over the next few days we can do the same thing again.”
Although they could not regain the yellow jersey Froome lost on Thursday, Sky put considerable pressure on Aru’s Astana team, which suffered another loss midway through the stage when Criterium du Dauphine winner Jakob Fuglsang abandoned.
The Dane had ridden for the best part of two days with fractures in his elbow and hand following a stage 11 crash.
It was a first career Tour stage win for Barguil, who has been out of form after he was one of six members of his team struck by a car during a training ride in January 2016.
“It feels really special,” the 25-year-old said of the win. “I’ve had two bad years behind me. Now I can show my real level again. I’m really happy.”With the top four watching each other closely, Irishman Dan Martin of Quick-Step Floors slipped away and was soon followed by Simon Yates in the young riders’ white jersey, and the pair picked up nine seconds by the finish line.
That leaves Martin in sixth place overall.