Playing without Nat Fyfe, Sean Darcy and Matt Taberner, the Dockers recorded their fifth-straight victory
Meanwhile the Cats fell to 4-3 to suddenly look vulnerable in the bottom half of the top eight.
It had all the makings of another Cats domination at GMHBA Stadium early after the hosts kicked the first three goals.
But the Dockers fought back hard to even the scoreboard at the half-time.
Fremantle continued to push in the third quarter — extending its lead to three goals— while keeping the Cats goalless for nearly an hour of game play.
The Dockers then withstood a late fightback from the Cats, who kicked two goals late in the game, to hang on for a famous victory.
The Cats had all the play in the first quarter, booting the opening three goals through Tom Hawkins, Tyson Stengle and Mark Blicavs to put pressure on the visitors.
Iowa State running back Breece Hall selected by New York Jets