The hosts headed into Monday's fixture without a win from their last six La Liga outings, while Espanyol were looking to build on last week's 3-1 victory against Villarreal in the Copa del Rey.
But it was the home side who cruised to an impressive victory, their first since November, to move six points clear of safety and above their opponents in the table, with Espanyol, who failed to register a shot on target, now looking nervously over their shoulder.
Eibar were on top from the kick-off and Sergi Enrich struck after 24 minutes with his fifth goal of the campaign to give the hosts a well-deserved lead.
Pablo de Blasis then doubled Eibar's lead when he netted seven minutes after half-time before substitute Charles completed the victory in the closing stages.
Eibar are now 11th in La Liga, with Espanyol dropping to 13th.