I think this season Sevilla was very lucky to defeat Manchester United . Manchester United have done well in their performance this season, Sevilla was just lucky that the time they met with Manchester united , Manchester United was in their worst state , some players were on injuries and other mistakes that led to the defeat of Manchester United.
But I think it's not just luck, because Manchester United also difficulty in previously a few seasons to win against Sevilla. Look at the head to head history of this both teams if Sevilla are lucky, so they don't have a good record with four wins in the last seven meetings against Manchester United including this match.
Next Sevilla will against Juventus in semifinals, after beating Mancheter United very well, maybe they will qualify for the finals too. But Juventus which also won against Sporting before, making them even more confident to win against that Spanish team.