The match could have been made intriguing early on, but Mikel Oyarzabal skied a penalty in the opening minutes after Dan James had committed a needless foul.
Bruno Fernandes and Anthony Martial both went close for United, the former hitting the crossbar with a long-range chip, while La Real centre-back Modibo Sagnan also struck the woodwork with a fine header after half-time.
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United had one or two more chances to get themselves on the scoresheet and Axel Tuanzebe was denied a first senior goal by a VAR review calling a foul by Victor Lindelof, but the outcome of the tie was assured last week and the draw mattered little.
Here are five things we learned from Thursday night’s game.
A healthy first-leg lead allowed Ole Gunnar Solskjaer to rotate a few names, though perhaps there were more starters in the line-up than might have been expected.
Of those coming in, Alex Telles and Dan James didn’t really forge an instant understanding down the left flank, the latter gifting a penalty early on,
Eric Bailly also came in at the heart of the defence, giving an interesting chance to see him directly alongside his real competitor for a starting berth, Victor Lindelof.
The former Malaga defender was excellent throughout, as he has been in the majority of his displays - it’s just the ongoing issue of having him available to select more often.
There has been plenty of talk in the last couple of weeks about Man United’s future No. 1, mostly rumour-generated chatter about potential transfer roundabouts.
David De Gea has failed to entirely convince again this season, Dean Henderson has been reported as being unhappy with a relative lack of game time and the likes of AC Milan’s Gigi Donnarumma have even been mentioned as summer targets for a total overhaul.
Here, Henderson once more did all he could to press his case - though that was relatively little, in truth.
He wouldn’t have saved the header against the bar or the penalty, but neither were on target - and neither was anything else Real Sociedad managed until the 85th minute.
Two second-half changes for Man United would have pleased watching supporters, as the next generation got another chance to show their worth.
Recent arrival Amad was brought on midway through, showing a few flashes of that blinding acceleration on the turn and ability to dribble past defenders.
Perhaps more pertinently, Shola Shoretire came on aged 17 years and 23 days, to become the club’s youngest-ever player in a European match, eclipsing the long-set record held by Norman Whiteside.
La Liga challenge
What’s next for Real Sociedad? The small matter of travelling to Real Madrid in La Liga on Monday night.
La Real are fifth in the table and have found form of late, winning three in a row, but they are seven points off fourth-place Sevilla so a positive result is required if they hope to keep the pressure on to challenge for a Champions League spot.
Otherwise, Spain’s quartet for next term looks almost set already, and the San Sebastian side will once more compete in the Europa League.
Given the evidence in the knock-out phase here, that’s the limit of their current level in any case.
For United, it’s a similar challenge in a top-four rival: they face Chelsea away on Sunday, and while it’s the Red Devils who are comfortable in second and six points above the Blues, they haven’t exactly been in consistent form of late.
Ole Gunnar Solskjaer will need to ensure a much more solid, all-round performance in that game than has been shown recently in domestic matches - and this midweek game was much more of a gentle stroll than a real warm-up for it.
It was job done at half-time in this particular tie and United won’t take much more from it than the fact nobody got injured and a couple of players enjoyed a rare run-out, and maybe those are the only positives needed in a crowded portion of the season.