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Well, Sevilla have started this season just as bad as they did last season, i don't know where you got the impression that they are performing very well, they have played three games in La Liga this season and they have lost all three of them and they are rooted in the bottom of the table.
Having said that, it is going to be somewhat difficult for Sevilla to make it out of Groub B in the CL, but their fans might not mind if they crash out and into the Europa league, because they have a knack of winning that competition.
Basically there will be 6 matches that Sevilla will play in the Champions League group stages this season and I am sure some of them are still very difficult to predict. I'm not ruling out a good possibility for Sevilla in the group stage even though actually the average person thinks they won't qualify for the next round. Sevilla had chances although not as good as other teams, but we never know how they took advantage of those opportunities before they started their game.
Sevilla's main focus remains to qualify for the round of 16, but dropping to the Europa League is no big deal either. Sevilla have proven time and time again that they are the team to be feared the most in the Europa League instead of the Champions League, so there are certainly a number of things they can consider, including which to prioritize the most.