Gorka Guruzeta and Nico Williams struck second-half goals to deservedly secure the points for Los Leones, who dominated at a jubilant San Mames.

Atletico have lost four games in La Liga this season, each away from home, while winning all eight matches they have played at their Metropolitano stadium.

"We cannot play like this, one way at home, another away, you can't win titles like this, you can't win leagues," Atletico goalkeeper Jan Oblak told Movistar.

Ernesto Valverde's Athletic tested Oblak frequently, with brothers Inaki and Nico Williams both striking the woodwork, while Oihan Sancet skied a penalty.

Inaki Williams, making his 400th appearance for Athletic, helped create the opener, finished by Guruzeta from Ander Herrera's cross.

Nico Williams added a stunning second when he bent a shot over Oblak into the far top corner with his weaker left foot.

Despite defeat and his team's drab display, Atletico coach Simeone maintained a positive attitude.

"Today is the day I am calmest," he told reporters.

"I know the boys are giving me (everything) and I am with them to the death."