History was made in the East End of Glasgow as Inverness CT won their first-ever league match at Celtic Park.
Billy Mckay was the headline-maker, turning in a cross to create another Champions League hangover for Celtic.
Neil Lennon's side have now lost two out of their last three home league matches, with the other a draw, all after midweek European matches.
But focus should be on the visitors as only the bar and a goal-line clearance prevented a more emphatic win.
Not that Celtic did not have chances; they just could not take any.
Mikael Lustig, Kris Commons and Georgios Samaras were the chief culprits on a day when nothing much went right for the home side.
And what a transformation in Caley Thistle. Could this really be the same side who shipped five goals to Motherwell last week?
Despite a promising start for Inverness, the first serious chance of the match fell Celtic's way; an excellent short pass from Beram Kayal sent Lustig into the area but, rather than shoot, he tried to cross and the opportunity was wasted.
Victor Wanyama tried his luck with an effort from outside the area but the shot was easily held by Antonio Reguero in goal.
Just before the half-hour, Inverness got into their stride and a strong run from Owain Tudor Jones from midfield created some space for the visitors' Andrew Shinnie but he totally miscued his strike wide.
Commons squandered a wonderful chance to put Celtic ahead. Played in by Gary Hooper, his right-foot shot went horribly wide. He would go on to have an afternoon he would rather forget.
As Celtic picked up the pace, Lustig should have put his side into the lead after being played in by Beram Kayal, but he side-footed straight into the side netting.
After a goalless first half - and, one would imagine, a bit of a dusting down from manager Neil Lennon - Celtic had the first chance after the break but the sight of Commons with his head in hands reflected his high blast over.
As Inverness grew in confidence, and pressed in the opening period of the second half, Efe Ambrose almost put into his own net for Celtic from Aaron Doran's cross.
But the Inverness threat would not be blunted for long and, on 64 minutes, just as Celtic prepared to bring on Paddy McCourt for Tony Watt, Philip Roberts broke down the right wing and checked back inside to flummox two Celtic defenders, before firing over a cross which was touched in by a grateful McKay.
Minutes later, Inverness created another chance but Jones just could not get a touch to another cross from the Celtic left.
Samaras then wasted a wonderful chance for Celtic, as his header was saved by Reguero when he really should not have been given a chance to reach it.
Inverness were good value for their lead - which should have been doubled when Billy McKay was played in again.
He watched his curling effort come back off the crossbar, and expected, as we all did, that Aaron Doran would bury the rebound, with keeper Fraser Forster stranded.
However, a split-second hesitation before shooting allowed Efe Ambrose to make a magnificent goal-line clearance to keep the deficit to one, and retain a glimmer of Celtic hope.
That petered out in three minutes of stoppage time, after which the Inverness players, and their delighted manager Terry Butcher, took a well deserved curtain call in front of a small band of ecstatic fans who have now seen their side win in the League Cup at Ibrox and, for the first time ever, at Celtic in the league.