The Italian rider won the 160.5km fifth stage at La Planche des Belles Filles by 16 seconds from Ireland's Dan Martin to move up to third overall.
And it was on that very same climb in 2014 that Nibali had tasted victory before going on to dominate, and win, the Tour title.
AS with Nibali three years ago, Aru also did so whilst wearing the Italian national champion's jersey.
"I'd never climbed it before but of course I saw that last climb on the internet when Chris (Froome) won in 2012 and Nibali in 2014, so that's why I decided to attack with 3km to go," said Aru.
Back in 2014, Nibali had no peers as Froome, who now leads the Tour after finishing third, and Alberto Contador had both crashed out of the race.
Briton Froome rolled over the line in third at 20sec, just ahead of Porte, to take the race leader's yellow jersey off his compatriot and team-mate Geraint Thomas, who drops to second, although at the same 12sec gap that he previously enjoyed.
Aru, though, is now just 14sec back and Froome said he and his Sky team-mates would not be able to take their eyes of the Sardinian again.
"Fabio rode a great stage and attacked at just the right moment before the climb flattened out before the last kick," said the 32-year-old Briton.
"If anything, behind we gave him a little too much space. After I made my move, three or four guys followed me but no-one really wanted to pull on the flat part.
Nairo Quintana was the biggest loser of the day, coming in 14sec behind Froome, leaving him ninth overall at 54sec.
But with the top 10 separated by a second over one minute, and all the contenders in there, the race is now truly on.