Following the death of Queen Elizabeth II earlier in the evening, both sets of players wore black armbands and a minute’s silence was impeccably observed by all those inside the ground ahead of kick-off.
UEFA decided it was too late to postpone the fixture but Old Trafford was understandably below full capacity and a subdued atmosphere reflected the mood of the nation. Announcements were low-key, while advertising boards were black with branding toned down.
The game’s only goal was scored on 59 minutes in controversial circumstances. Lisandro Martinez, introduced as a half-time substitute, was deemed to have handled the Casemiro in the box as he blocked a close-range David Silva shot, despite the former Manchester City midfielder’s effort deflecting off the Argentine’s thigh first.
Italian referee Marco Di Bello immediately awarded a penalty and after being checked by VAR, his decision stood. Brais Mendez stepped up to give Sociedad the lead, his powerful and precise spot-kick too good for David de Gea.
Cristiano Ronaldo, who was back in the United starting line-up for the first time since August 13, earlier thought he had put his side ahead, but his powerful header from a Diogo Dalot cross in the 36th minute was correctly ruled out for offside.
The 37-year-old saw two more efforts miss the target after the break before Sociedad went in front. Casemiro – making his full United debut – then had a shot from distance well saved by Alex Remiro as the hosts went in search of a late equaliser.
It didn’t arrive though and Erik ten Hag, who made six changes to his team following Sunday’s victory over Arsenal, loses his opening European fixture as United manager.
United are third in Group E after matchday one, with Sheriff Tiraspol beating Omonia Nicosia 3-0 in Cyprus in the evening’s other game.
It is the first time Sociedad have won against English opposition in European competition, while United had not lost at home in the Europa League for 18 matches before Thursday’s defeat.
However, the result prompted a muted response from both players and staff on the sidelines at the final whistle in light of the sad news from Buckingham Palace.