Bruno Fernandes and Manchester United led the way on an incredible night of European football for English clubs.
The United skipper and talisman scored twice in a 3-0 triumph in Bilbao as United turning their poor Premier League form on its head and all but secured a return to the Basque city for the Europa League final on May 21.
It should be an all-English affair after Tottenham defeated Norwegian minnows Bodo/Glimt 3-1 in north London with goals from Brennan Johnson, James Maddison and Dominic Solanke.
In the Conference League, Chelsea eased to a 4-1 victory at Swedish side Djurgarden with Nicolas Jackson netting twice.
United head coach Ruben Amorim warned against complacency after a dramatic 16-minute spell before half-time saw his team score three goals and Athletic Bilbao have a man sent off.
‘Nobody expected this result but it’s not done,’ said Amorim. ‘The same result can happen at Old Trafford, and we need to be prepared.
‘There is no away goals (rule) so anything can change and that is my message to the players.
‘I think they have to think about the second leg, and they have to think more about the first 20 minutes than the rest of the game. We struggled a lot at the start but the goal and red card changed the game.’
Bilbao boss Ernesto Valverde was angry that Norwegian referee Espen Eskas decided to send off Daniel Vivian for a foul on Rasmus Hojlund and award a penalty converted by Fernandes – even more so because it looked like Alejandro Garnacho had handled in the build-up.
‘It's been too much of a punishment, not only by the fact that we went 2-0 down but because we had to play with one man down,’ said Valverde.
‘We have challenged a handball by Garnacho, but it’s the ref who needs to referee.’