With 11 minutes left at Celtic Park, the hosts were two more matches from the Champions League group stages. Then it all went horribly, horribly wrong.
Cluj scored to put themselves in front on away goals, then did so again in stoppage time in front of an aghast Celtic support. It left manager Neil Lennon talking almost disbelievingly about his side now having to "make sure we qualify" for the Europa League.
But how much has this defeat - a second in the third qualifying round in two seasons - cost Celtic financially? And how much has it cost Scottish football?
Had they held on, then edged past Slavia Prague in the play-off round to reach the Champions League group stage, Celtic would have been guaranteed 15.25m euros (£14.13m). Instead, should they progress past AIK of Sweden or Sherrif Tiraspol of Moldova in the Europa League play-offs, they will pick up a comparatively paltry 2.92m euros (£2.71m).
That is the thick end of £12m gone already. But the haemorrhaging does not stop there. As the table below shows, the difference in money received for picking up points in the respective competitions is stark. So, too, is the bounty on offer for reaching the knockout stages.
Then there is Celtic's share of the coefficent ranking pot. That would have been at least another 1.1m euros (£1m), based on where the Scottish champions would have ranked among the 32 teams in the groups. In the Europa League, that payment would range from 71,430 euros (£66,000) to 3.42m euros (£3.17m) - but the latter would only be claimed if Celtic were the highest-ranked team in the competition.
It depends. Failing to reach the Champions League group stages has cost Celtic an automatic four coefficient points for starters, but George Tucudean's goal seven minutes into injury time for Cluj also denied them the half point they would have earned for drawing on the night. That might seem insignificant, but one more draw last season would have nudged Scotland up from 20th in the rankings to 19th.
A similar scenario unfolded in the early weeks of last season, though, and Scotland still went on to enjoy a stellar campaign. Both Celtic and Rangers competing in the Europa League group stages helped earn the nation's biggest points haul for 11 years of 6.75 and bumped the country above the likes of Sweden, Poland and Belarus.
This term has started strongly, too, with Celtic, Rangers, Kilmarnock and Aberdeen winning 12 of their 18 matches so far. That means 13.5 points are already on the ledger to give a coefficient of 3.375 - which current stands above any other nation in the continent. A strong position on which to build, then, and with three teams still in the Europa League.
John: "Central midfield most certainly was a problem. Why? Because the best central midfielder at the club was playing left-back! Neil Lennon hasn't a notion."
Jock: "Callum McGregor is no left back. Huge loss in his natural position. Can't understand why we had £10m worth of defenders on the bench watching this calamity unfold."
Mike: "Neil Lennon, you have to take blame on this one. Wrong decision to play your best playmaker at full back. Then take lead again at 3-2 and still lose."
Zayne: "Defence still needs fixing. If Cluj can score four goals at home then spend some money Celtic. There are good teams in The Europa League if we do qualify."
Sean: "Just have to open up the cheque book and strengthen again before the window closes, and concentrate only on retaining the league title."
Alan: "Brendan Rodgers sowed the seeds for this chaos with short sighted loans and no forward planning for the defence."