This was a typically familiar United, holding on, making it hard and squeaking - by inches - over the line and into the final.
It was functional, fraught and not flashy but United, as they've done so often, diced with death and just about did enough to get the job done and set up a final with Ajax.
On this evidence, though, the performance levels will need to be much improved to overcome Peter Bosz's vibrant and energetic young side in Stockholm.
The most explosive moment of the night came during the late melee that led to Eric Bailly's sending off and subsequent suspension for the final.
Some are questioning Mourinho's suitability at the club when it should not be forgotten that Sir Alex regularly embraced pragmatism.
Nine years ago, on the way to a league and European double with a team considered his finest, United's brave and resilient rearguard clung on against a daunting and vastly superior Barcelona side (having settled for a goalless draw in the first leg).
Jose and Ferguson are both capable of mixing things up and it's this adaptability that sets them apart from many of their managerial peers.
Jose reverted to type against Celta but yet could still end the season with two trophies and coveted Champions League qualification, a campaign that would have to be considered a success.
But when we deploy grit over guile and resilience over ruthlessness against a mid-table Spanish side - albeit one that have beaten Barca and Real this term - with a team worth almost £200 million, then there is something fundamentally flawed.
United edged past Rostov in regulation time and needed an extra 30 minutes to see off Anderlecht last time.
Indeed, none of the knockout wins in Europe, with the exception of Saint Etienne, have come by more than one goal and that hardly resembles the potent and free-scoring form of potential Europa League winners.
As we've seen so often this season, the players seemed gripped by fatigue and nervous anxiety in the last 20 minutes as Celta swarmed forward.
Mourinho could be seen frantically waving his side up the pitch, a sign that he had not intended for us to sit deep and invite pressure.
He was noticed instructing Jesse Lingard and Henrikh Mkhitaryan to offer more going forward and Marcus Rashford to stay up top as United sat deeper.
That suggests that the reticence does not come from the touchline but that there's a psychological cautious instinct - maybe even fear - holding the players back.
At this stage of the season, results are all that matter and United need to banish any mental demons with one more big hurdle to overcome in Stockholm.