O'Connor (centre) scored his first goal since returning to Hibs
Garry O'Connor's stoppage-time goal gave Hibernian their first-ever triumph in Inverness as Caley Thistle were made to rue a string of missed chances.
Caley Thistle's Gregory Tade had an effort ruled out for offside.
Hibs' Ian Murray had a similar effort chopped off before Matt Thornhill was denied by a Ryan Esson save.
Caley Thistle's Greg Tansey struck a post before Esson somehow allowed a scuffed shot from O'Connor to cross the line in the dying seconds.
And defeat leaves Inverness as the only side still to secure a point in the Scottish Premier League.
Two of Caley Thistle's three most recent signings, Wales midfielder Owain Tudur Jones and Austria Under-21 full-back Thomas Piermayr, had come into the starting line-up in place of Andrew Shinnie and David Proctor.
David Stephens replaced the injured Sean O'Hanlon in the visiting defence, which was the first to be under pressure after a quiet start.
Piermayr's 25-yard drive flew just wide of a Hibs post and the visitors responded immediately, with Kenny Gillet's last-ditch tackle turn.
However, it soon became clear why Inverness manager Terry Butcher was so keen to re-sign the experienced Chris Hogg on Friday.
With Hogg not yet match fit, his former team were finding their way through the home central defence and Kenny Gillet denied Ivan Sproule with a last-ditch interception after the winger delayed his close-range strike.
Esson beat away a 20-yard drive from O'Connor and the Scotland striker was denied again when his side-foot effort from just three yards following a Sproule cross struck the goalkeeper on the face.
Butcher was berating his players in frustration and they responded with a half-volley sent over the crossbar at the back post by Richie Foran.
As Caley Thistle showed signs of improvement, Tade had the ball in the net, smashing the ball home from close range, but his celebrations were cut short by an offside flag against Foran.
Inverness continued to improve after the break, but the officials came to the rescue of Caley Thistle after Murray smashed the ball into the net from six yards only for the goal to be chopped off thanks to a flag from the assistant referee.
Hibs took heart and Esson did superbly to turn a Thornhill scissor kick over the crossbar.
Tansey poked the ball just wide from close range after a good run by the Inverness midfielder, while Tom Aldred failed to connect from only two yards as a cross flashed across the face of the Hibs goal.
Hibs goalkeeper Graham Stack parried clear a powerful effort from Shane Sutherland, while Tansey struck the post from close range, but the visitors stole the points in stoppage time.
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