You are right because Chelsea might be channeling all there attention to their champions League game against a Spanish giant ( Real Madrid) so they can be distracted in games like this that don't have significant, they are well okay in the league and they can't challenge Liverpool and Manchester City right now for the title so they need put there energy in a competition they can still win while arsenal lose will be dissapointed because the game is very essential in their quest to go to the champions League.
Apart from that Chelsea are not targeting anything in the Premier league for the title they are not able to compete
and for the champions league tickets are safe so don't be surprised sometimes there are surprises in the Premier League.
As you said the Champions League will be their focus this month especially have to fight a strong team.