Two goals from Kris Doolan were enough to give Partick Thistle a 2-1 victory in the Highlands as the visitors inflicted a first home defeat of the Scottish Premiership season on Inverness.
Doolan opened the scoring in the 19th minute with a fine finish from close range but Inverness, who had a goal right on the stroke of half-time controversially ruled out for a supposed foul following a corner, drew level in the 46th minute courtesy of Gary Warren's header.
Partick, however, claimed all three points in the 82nd minute, goalkeeper Dean Brill failing to hold a deflected cross which gave Doolan the chance to prod home the winner.
There were two changes from the Inverness side that had lost 4-0 at St Johnstone before the international break.
David Raven returned from a groin strain to replace Daniel Devine, while Ben Greenhalgh came in for his first start at the expense of youngster Liam Polworth.
For Partick, James Craigen was preferred to Steven Lawless from the side which had gone down to a 1-0 loss at home to Hibernian in their previous outing.
Caley Thistle were looking to close the gap to just a point on league leaders Celtic and they went close early on, Aaron Doran's free-kick from 18 yards curling just wide.
Doran then turned architect moments later, playing a delightful ball over the top for Greenhalgh to run on to, but his fierce drive from eight yards rebounded to safety via the base of the post.
Inverness were looking the better team going forward, yet it was Partick who took the lead in the 19th minute.
Kallum Higginbotham's ball sent Craigen driving into the home penalty area. His low cross picked out Doolan at the near post and the forward took a neat touch before firing into the far corner.
Caley Thistle's response to conceding their first goal at home this season was a positive one.
Firstly, Ross Draper's stinging drive from 20 yards was touched over superbly by Partick goalkeeper Scott Fox, before the custodian was called on again minutes later to keep out Doran's low effort from the edge of the box.
Partick were posing a threat on the break and Craigen may have felt he should have done better than firing well over from 22 yards when given both time and room to shoot.
Inverness felt they had equalised right on the half-time whistle as Doran's strike from 16 yards found the target after Billy McKay had seen his effort blocked by Sean Welsh on the line, but it was ruled out for what the match officials deemed to be an infringement from the corner in the build-up to the goal, despite television pictures seeming to suggest otherwise.
That sense of injustice seemed to spur Caley Thistle on and they equalised barely a minute after the interval.
Doran's free-kick from the left found Gary Warren rising highest above everyone inside the six-yard box to power home a leveller that, on balance of chances alone, the hosts merited.
McKay was then denied a goal to give Inverness the lead, Aaron Muirhead putting in a timely block, before Josh Meekings' challenge at the other end prevented Doolan from getting his shot away when clean through.
Caley Thistle then had the ball in the net from a Doran corner, but Richie Foran's header was ruled out for pushing in the build-up.
Foran was then set up by McKay following good work by Doran, yet the Inverness captain sent his placed effort well over from 20 yards.
The home side continued to force the issue in the latter stages, McKay just inches away from connecting with a cross by substitute Marley Watkins.
But it was Partick who regained the initiative with just eight minutes of the game remaining. Welsh sent Aaron Taylor-Sinclair surging down the left and his cross took a deflection off Warren deceiving Brill, who could not hold the ball which fell kindly into Doolan's path and he could not miss, tapping home his third goal of the season.
Warren had a late chance in injury-time for Inverness, but his header went narrowly over as Partick clung on to take the victory.