Ryan Christie scored one, set up another and was later sent off as Inverness won 2-1 to end Aberdeen's 100 per cent record in the Ladbrokes Premiership.
Miles Storey was teed up by Christie to open the scoring before the home-grown midfielder buried a terrific effort from long range to double the hosts' advantage.
Ashton Taylor pulled one back before half-time but a dogged second-half display from Caley Thistle saw them hold on to take three points.
Christie was sold to Celtic in the summer but loaned back and his efforts on the day did his parent club, the Dons' title rivals, a favour. He was dismissed in stoppage time for his second yellow card, both for fouls on Graeme Shinnie, but it had no effect on the outcome.
Inverness made one change from the side that beat Livingston 2-0 on Tuesday night, with Liam Polworth replacing Carl Tremarco. The latter joined Richie Foran and Dani Lopez in missing out on the matchday squad.
The Dons made three switches from their League Cup exit to Hibernian. Willo Flood, David Goodwillie and Adam Rooney made way for Paul Quinn, Jonny Hayes and Josh Parker.
Kenny McLean had the first effort of the game low to Owain Fon Williams' left, but the goalkeeper got down to keep out his shot.
But it was Caley Thistle who took the lead on eight minutes after superb work by Christie. He executed a perfect drag-back and turn to fool ex-Caley Thistle captain Shinnie before playing in Storey, who took a touch to compose himself and unleashed a curling shot that flew beyond Danny Ward.
The visiting Dons, with eight wins from eight league games before this one, were struggling to cope with the lively hosts as Ross Draper was denied only by Paul Quinn's block. When Ward flung out a hand to deny Polworth, Aberdeen were on the ropes.
With half an hour gone the Caley Jags were two up, thanks to a wonder-strike from Christie. The midfielder made space for himself 30 yards from goal and let fly, his shot looping over the stranded Ward.
Derek McInnes needed to see a response from his beleaguered side and Taylor delivered it 10 minutes before the break. Another former Inverness favourite, Jonny Hayes, supplied the corner and an unmarked Taylor powered his header in.
Caley Thistle were not deterred, though, and another first-class save from Ward kept the deficit to one. Storey's clipped cross evaded the head of Andrew Considine to find Christie, whose downward header was superbly tipped around the post by the on-loan goalkeeper.
The second half saw the visitors put more pressure on the Inverness goal but they were still struggling to test Fon Williams. Parker embarked on a mazy run through the opposition half before ballooning his strike into the crowd.
Substitute Peter Pawlett smacked a free-kick off the far upright and Danny Devine cleared a Goodwillie cross off the line but the Dons were unable to breach Fon Williams' goal again.
Christie was shown his second yellow in the closing stages before Goodwillie skewed a glorious late chance wide.
Source: PA Sport