When Ole Gunnar Solskjaer walked towards the tunnel applauding the supporters after losing 2-0 at home to Paris Saint-Germain in the Champions League last month, there was a feeling his bubble had finally burst.
In the 11 matches which preceded that defeat, there was but one blemish – a 2-2 draw with Burnley – to Solskjaer's record as United boss. They'd been almost perfect, both in results and performances.
However, the manner of the loss to PSG, a comprehensive and surgical dismantling in their own backyard, suggested the so-called honeymoon period was over, as United came crashing back to the reality that they were still light years behind Europe's leading teams.
Solskjaer headed into the bowels of Old Trafford on that February evening looking ruefully helpless – there was only so much he could do.
But, as it turns out, there is so much he can do.
Rewind almost exactly a year, Jose Mourinho attempted to convince supporters, journalists and pundits alike that United's Champions League exit to Sevilla was not a shock.
"We went out to a side that's more successful than Manchester United in last seven years in Europe," he said last March. "Do you think they didn't have any players who could play direct in my team?"
Then, a few days later, came the infamous and bizarre "football heritage" monologue, in which Mourinho essentially blamed United's exit on inheriting a squad from Louis van Gaal which had a lack of experience in the Champions League.
It might have washed had United not gone out to a side who had never been beyond the last 16 of the competition, but in reality Mourinho only served to highlight just how poorly he suited the club.
"It's never mission impossible"
Had Solskjaer gone into Tuesday's pre-match news conference and written United off – given the fact no team had ever progressed in the Champions League knockout phase after losing by two or more goals in a home first leg – few would have blamed him. After all, he was without 10 first-team players.
Again, he could have focused on PSG and the talent at their disposal, juxtaposing their embarrassment of riches with United's necessity to name five youth team players in the travelling squad.
Instead, Solskjaer relished the chance to bring the youngsters and was bullish, saying everything one would expect of a Manchester United manager.
"Everyone expects us to go out and easily, but that doesn't happen with Man United," he said. "It's never mission impossible, it's more difficult, but we have got to get the first goal and then anything can happen. As a club we've done it so many times."
If anyone knew what was possible, the scorer of United's winning goal in the 1998-99 Champions League final did. Football heritage, anyone?
"Ole's at the wheel, tell me how good does it feel"
United arrived in Paris on Tuesday with academy kids in tow and – seemingly – all the belief in the world.
Few could have predicted what was to come, however, as United astonishingly went into the break 2-1 up thanks to a Romelu Lukaku brace – helped by errors from Thilo Kehrer and Gianluigi Buffon.
Although many have criticised the use of the VAR for the decisive Marcus Rashford penalty, the 21-year-old still had to make the most of it, and he did so by blasting emphatically beyond one of the greatest goalkeepers of all time. It looked routine, yet the outcome was anything but.
When Solskjaer is surely appointed as United's next full-time manager, Rashford's penalty and the historic nature of the turnaround will have been pivotal.
"Ole's at the wheel, tell me how good does it feel," goes the popular chant United are turning into an Old Trafford staple.
Having banished the negativity of Mourinho, restored United's identity and overseen one of the club's greatest Champions League moments, Solskjaer's not only at the wheel, he's slamming on the throttle and leaving the dark post-Alex Ferguson era way behind in the rear-view mirror.