⭐ Merited by The Pharmacist (4)
Sevilla played quite well, they were even able to kick Man United out of UCL.
I'm not surprised if Sevilla could kick Man United since Man United has no defenders. 
I think it will be more interesting to talk about "why Sevilla can be defeated by West Ham in Europa League?".
If they look downhill I think there is something lacking in the team so they cannot perform stable.
Of course, the huge decrease in Sevilla performance must have a reason. I don't see a problem in squad depth, so it is not true if players' fatigue is the reason since they can rotate the player composition (formation). The problem may be on players' mentality, the strategy, bad team works, or any other things. Well, whatever the reason is, simply it is related to lacking something in the Sevilla team.