Yes, given that Sevilla has collapsed and Atlético are still looking for their game, any place below second is vacant for any team. Especially at the start of the season, when the factor of easy calendar and "luck" plays a big role. The further the championship goes, the more familiar the standings will take (although I'm not sure that Sevilla will be able to return to the top half).
Yes, Sevilla's decline in performance compared to last season made the match an advantage for Atletico Madrid. Marcos Llorente scored for Atletico Madrid's advantage in the 29th minute. Sevilla really looked difficult in this match despite having a lot of ball possession, even Atletico Madrid were more likely to score goals. I don't expect Sevilla to win this game even though they are playing at home. They still haven't been able to rise from their slump so far.