Caley Thistle suffered a crushing first home defeat of the season, with a 4-0 loss against Partick Thistle.
A double from Ryan Stevenson, as well as goals from Gary Fraser and Conrad Balatoni inflicted the damage on an Inverness side that looked a shadow of their usual selves, but nevertheless remain in second place.
Caley Jags manager John Hughes stuck with the side that defeated Dundee 2-1 at Dens Park last week, meaning match winner Ryan Christie remained on the bench.
Partick made two changes from the side that drew 1-1 with Kilmarnock on Saturday, with Jake Carroll sidelined through injury and James Craigen relegated to the bench, meaning returns for Jordan McMillan and Gary Fraser.
Inverness were looking to avenge for a 3-1 defeat against Alan Archibald’s side at Firhill in September, but passed up a glorious chance to take the lead on nine minutes when Marley Watkins was released by Billy Mckay, but dragged his shot wide of the right-hand post.
Partick duly punished them three minutes later, when Christie Elliott crossed low to the near post for Ryan Stevenson, who nipped in ahead of Dean Brill to prod home.
The hosts were limited to predominantly long-range shots in their search for an equaliser, and Thistle grabbed their second on 40 minutes when Gary Fraser cut the ball back for Stevenson, who tucked a fine 20 yard strike past Brill for his second of the match.
It could yet have been worse for the Caley Jags before half-time, with Brill performing heroics to beat away Danny Seaborne’s goal-bound header.
However, Inverness only survived four minutes of the second-half before their resistance to a third goal was breached, as Stevenson crossed for Fraser to head in off the crossbar.
Caley Thistle thought they had pulled a goal back minutes later when David Raven’s long-range shot found its way into the net through a ruck of bodies. Although the ball did not strike a home jersey, assistant referee David Wilson flagged for offside against a player he judged to have obstructed Gallacher’s line of sight.
Rather than hand Inverness a way back into the match, worse was to follow on 56 minutes when Conrad Balatoni headed past Brill from a Stuart Bannigan corner.