Steven Lawless scored the only goal of the game with just six minutes remaining to secure the victory at Firhill.
The game appeared to be heading for a tame stalemate when Lyle Taylor knocked the ball down to the Partick midfielder and he drilled a low shot into the corner past Ryan Esson.
Caley Thistle started brightly and home defender Conrad Balatoni was forced to make a timely intervention to prevent Graeme Shinnie hitting the target.
Ryan Christie then headed the ball across goal but Partick goalkeeper Scott Fox got down well to make the save.
At the other end a Stuart Bannigan corner was cleared back to the Partick midfielder and his second delivery found Kris Doolan but he headed over the bar.
The home side started to take a grip of proceedings and just after the half-hour mark James Craigen surged into the Inverness penalty only to be thwarted by Esson at his near post.
After the break Esson was tested again and this time the Caley goalkeeper had to tip a fierce free-kick from Ryan Stevenson over the bar.
The visitors were almost punished when Lawless disposed a dithering defender and slipped Doolan in, but his effort was blocked.