The red card received by Dani Vivian in the 33rd minute made the match lopsided, Bilbao were increasingly under pressure because they were outnumbered and had difficulty keeping up with Man United who were increasingly free to control the match.
I don't think that should have been a red card. If the last man commits a foul inside the box, it should be a penalty and a yellow card, but if it were outside the box, then it should be a red card. It should only be a red card and a penalty when the challenge would have been a red card regardless of where it happened on the pitch, last man or not.
To make things more interesting, there was a handball by Garnarcho that happened in the build-up of the penalty. That should have cancelled the foul entirely, but it was not called.
That's football for you, though. You can prepare all you want and be ready as you can be, but one bad decision can ruin your whole plans.
I think everyone thinks like you. Because I think the same way. I couldn't understand how the referee gave a red card for that move, most likely no one could understand, there was no hit, nothing that could injure the player, but he showed a red card directly.
With this red card, the fate of a team was determined.