Celtic's bid to reclaim the league title from champions Rangers got off to a nightmarish start on Saturday night, after they slipped to a 2-1 defeat to Heart of Midlothian at Tynecastle.
The newly-promoted hosts stunned the Hoops after only eight minutes, when Gary Mackay-Steven tapped home to round off some good work from Liam Boyce.
Celtic pushed to draw level, with David Turnbull going close on a number of occasions, but he failed to test goalkeeper Craig Gordon, and the visitors went into the break behind by a goal.
The Bhoys did not have to wait long after the half-time pause before finding a killer response, when Anthony Ralston danced through the Hearts defence with some brilliant, nimble footwork and calmly slotted the ball home from inside the box.
Liel Abada then had the ball in the net for Celtic, but his strike was ruled out for a very tight offside call. Hearts were under the cosh in the second half, and Gordon had to be at his best to deny substitute Ryan Christie.
And Celtic were made to pay for their wastefulness in front of goal, when defender John Souttar 'leapt like a prized salmon' - according to Hearts' official Twitter account - to stick a looping header beyond Scott Bain and into the back of the net.
The hosts saw out the final minutes of injury-time to claim a famous victory on their return to the SPL, simultaneously sinking their opponents to an awful defeat.
This disastrous result only compounds supporters' misery, after Celtic were knocked out of the Champions League in the second qualifying round by FC Midtjylland, meaning they will have to watch the elite European competition from the sidelines for another year.
New coach Ange Postecoglou's reign couldn't have got off to a worse start then, as he aims to knock Steven Gerrard's Rangers off their new-found perch at the peak of Scottish football.