Tiago Mendes' superb header just before half-time put Atleti ahead before Mario Suarez struck in the 71st minute to secure all three points at Estadio Vicente Calderon.
All eyes were on Diego Simeone's men after they stumbled to a 3-1 defeat against Valencia prior to the international break.
The duo's efforts lifted the Spanish champions to fourth, while their opponents dropped to 11th.
Atletico almost took the lead in just the second minute, Tiago flicking on Gabi's corner to the back post - where Arda Turan unleashed a powerful volley that forced Kiko Casilla into a stunning reactionary save.
Miguel Angel Moya, Casilla's opposite number, was pressed into action soon after, the goalkeeper producing a point-blank stop to deny Alvaro Vazquez from Sergio Garcia's fine centre.
Casilla was then forced to turn Koke's low strike around the post.
Atleti were particularly dangerous from set-pieces, illustrated by Tiago forcing Casilla into another save from Gabi's corner.
But Casilla could do little as Tiago opened the scoring after 43 minutes, looping a header into the far corner from Gabi's superb cross.
Diego Godin rose highest to meet Koke's corner, his header finding Raul Jimenez - who then nodded back across goal for Suarez to tap into an empty net when the ball already seemed destined to cross the line.
That seemed to take the wind out of Espanyol's sails, with the hosts almost adding a third when Griezmann rattled the outside of the post from a tight angle having rounded Casilla.
