The first three goals on the night came via the penalty spot as Mikel Oyarzabal had slotted Sociedad into an early lead.

However, Fernandes quickly restored parity and coolly scored again from the spot on 50 minutes.

The Portuguese international then ensured United will face Lyon in the last eight by firing home his 15th goal of the season.

Diogo Dalot rounded off the scoring in one of Ruben Amorim's best nights since taking charge of the Red Devils.

Languishing 14th in the Premier League and out of both domestic cup competitions, United's last remaining hope of salvaging a miserable season lies with the Europa League.

Amorim's men were roared on a by a 74,000 full house, although there were continued protests against co-owners the Glazer family.

Sociedad's season also hinged on European glory amid a disappointing La Liga campaign.

Imanol Alguacil's side made a positive start and got their reward when Oyarzabal was chopped down by Matthijs de Ligt as he attempted to reach Aritz Elustondo's cross on 10 minutes.

The Sociedad captain scored his side's equaliser from the spot as the first leg ended 1-1 last week.

Oyarzabal sent Andre Onana the wrong way once more to give a United side short on firepower a mountain to climb.

However, the Red Devils were level within six minutes.

Rasmus Hojlund's goal drought stretched to 21 games, but the Dane was fouled as he tried to reach Fernandes' ball across goal and the latter rolled home the resultant penalty.

United should have been in front by the break as Hojlund missed a glorious chance when he flicked Joshua Zirkzee's teasing cross wide.

The English giants had to wait just five minutes into the second period for another chance to win the tie.

Zirkzee could not beat Alex Remiro from the edge of the area, but Patrick Dorgu was first to the rebound and was adjudged to have been fouled by Elustondo.

Amorim said after Fernandes' stunning free-kick in Sunday's 1-1 draw against Arsenal that his side "needed more Brunos".

Not for the first time in a difficult season, the United skipper took responsibility to put his side in front.

Sociedad's task got even harder just after the hour mark when Jon Aramburu was shown a straight red card for bringing down the impressive Dorgu as he charged through on goal.

The only negative of the night for United was another goalless showing for strikers Zirkzee and Hojlund.

Zirkzee was denied again by Remiro before heading wide with the goal gaping.

Fernandes showed the poise in front of goal his forwards lacked when he drilled Alejandro Garnacho's pass into the bottom corner three minutes from time.

Hojlund did at least bag an assist late on as his cross was drilled high into the net by Dalot.