The Reds head into the game with the hope of avoiding a defeat in Spain and getting the job done at Old Trafford.
However, they found it easy against Bilbao, claiming a 3-0 victory and taking a huge advantage into the second leg.
As it happened
Athletic Bilbao played without their leading scorer, Oihan Sancet, with the team's attack spearheaded by Maroan Sannadi, Inaki and Nico Williams.
Manchester United's lineup saw two changes, with Victor Lindelof taking Luke Shaw's place and Manuel Ugarte coming in for Kobbie Mainoo.
Man United kickstarted the game with swift pace, scoring three goals in the first half and getting a Bilbao player sent off for a professional foul.
Casemiro got the opening goal, while Bruno Fernandes scored a brace to put the Red Devils in a comfortable lead.
In the second half, the Red Devils controlled the game and made sure the host did not get a goal until the final whistle.
The 3-0 win puts Ruben Amorim’s men at a massive advantage heading into the second leg at Old Trafford.