Three of the goals came inside the opening 23 minutes, with Inverness taking the lead when Aaron Doran found the bottom right-hand corner of the net after latching on to David Raven’s low cross.
However, Partick turned the match upside down in the space of four minutes.
First, Steven Lawless raced into the area before curling the ball past Dean Brill, as Inverness conceded their first goal of the season on 19 minutes.
And shortly afterwards the hosts were ahead as Kallum Higginbotham’s deep cross was headed into the bottom corner by Abdul Osman.
That was the way it remained until 18 minutes from time when Higginbotham sealed three points for Partick with a fierce low strike from outside the area after latching on to Lawless’s measured assist.
And the Jags should have netted a fourth goal in injury time when Kris Doolan missed from the penalty spot, after Raven had pulled the striker down – the kick was comfortably saved by Brill.