Ruben Amorim had wondered which Manchester United would show up. In the space of another remarkable European night at Old Trafford, two did. A passive, error-prone team were dismal for an hour. Then an inspired finish sent a side who looked to be stumbling and blundering their way into the Europa League final instead surging to it. Amorim’s schizophrenic side could yet end a historically bad season on a genuine high. When Athletic Club threatened a comeback that might have been outlandish even for the watching Sir Alex Ferguson, United had a couple of decorated trump cards to play. A man who set up the winner in a Champions League final and a serial Champions League winner took them to the Europa League showpiece. Mason Mount’s belated first Old Trafford goal, almost two years into his United career, cancelled out Athletic’s lead. His 50-yard finish into an empty net in injury time meant he doubled his tally for the club in one devastating cameo. Meanwhile, Casemiro, who had headed United into a lead in the San Mames last week, repeated the feat, stooping to meet Bruno Fernandes’ free-kick. Unleashed from the bench with Mount, Amad Diallo set up Rasmus Hojlund for the simplest of finishes. After scoring three goals in 15 minutes in San Mames, United had four in 19 at Old Trafford. And yet Athletic, like Lyon before them, had led at Old Trafford. United retain their status as the only unbeaten side in all three European competitions this season but they keep flirting with defeat. At times, they lived down to their manager’s lowly billing. Amorim had talked United down and, for much of the match, they seemed to prove him right. The side he said can lose their minds threatened to lose the game. Had Athletic got the second goal they almost conjured, there may have been a wider loss of composure. Amorim, though, merits credit for United’s rousing finish. The second half was one-way traffic until he introduced Luke Shaw, Amad and Mount, while moving Fernandes back into midfield. It was a strength in depth Athletic lacked. It brought an emphatic turnaround. The scoreline suggests otherwise, but the glory belonged to the losers, the sense a depleted group mounted a heroic effort. A club whose budget is dwarfed by United’s were without their four best players: the suspended defender Dani Vivian and three injured attackers in Oihan Sancet and Inaki and Nico Williams. For an hour, Athletic were relentless. Ernesto Valverde has his own traumatic experience of 3-0 first-leg leads in European semi-finals: his Barcelona then lost 4-0 at Anfield in 2019. His search for a cathartic remontada ended with another of his sides conceding four in England. Yet it had begun better. Just Mikel Jaureguizar’s third goal for Athletic was a special strike, a magnificent curler from 20 yards nestled in the top corner. United were culpable, Harry Maguire giving the ball away to Unai Nunez; after creating a goal with his unexpectedly slick skills on the right wing last week, Maguire redressed the balance with slack play on the edge of his own box. For a moment, United may have wished he was still masquerading as a right winger. Alex Berenguer began brightly, as he had at San Mames, and curled a shot over. As Athletic sought a second, Unai Nunez looped a header wide and Gorka Guruzeta flashed a shot just past the post. Meanwhile, United had begun camped behind the ball, but too slack in possession and, when given the opportunities to counter-attack, missing the delivery, or the touch, or the timing of the run. When they got all three, Patrick Dorgu delivering a defence-splitting pass in an otherwise erratic display, Alejandro Garnacho dinked a shot wide. But Amorim turned problem solver. He has invariably said that Mount is a player he loves; the former Chelsea man showed why with a deft turn before curling a shot into the net. His second was glorious, latching on to a poor pass from Julen Aguirrezabala, which left the goalkeeper stranded outside his box, to find the empty net. Over the two legs, Fernandes and Casemiro made the biggest contributions to taking United on, scoring two goals apiece, and they combined for their second on the night. Hojlund, another who had looked out of sorts, was given a tap-in. Once again, it felt cruel for Athletic. Their hopes of a hometown final felt extinguished last week, but neither the spirited players or the vocal fans showed it. The raucous Bilbao supporters had travelled in their thousands, but there will be a Mancunian invasion of the Basque country later this month. The temptation is to say that United will need to play rather better on their return to the San Mames than they did in the first hour here. Although, as they are facing Tottenham, maybe they won’t.