Atletico Madrid sensationally thrashed their city rivals 4-0 on Saturday and second-placed Barca took full advantage of their old enemy's humiliation to reduce the gap to a single point.
Lionel Messi chalked up his 23rd league goal of the season via a deflected free-kick and Luis Suarez's 26th-minute strike set Luis Enrique's men on the road to a first win in four attempts in Bilbao.
The hosts retained attacking ambition and pulled a deserved goal back after the break through Mikel Rico but an own goal from Oscar de Marcos and a sublime Neymar strike in quick succession put the result more or less beyond doubt - even if it was Athletic striker Artiz Aduriz rounding off a frantic period of four goals in seven minutes.
Xabier Etxeita was deservedly sent off for a shocking 75th-minute lunge on Suarez, leaving Barcelona to close out victory with a fantastic fifth in the 86th minute - Messi showcasing mesmerising footwork to feed Sergio Busquets, who crossed to give substitute Pedro Rodriguez a tap-in.
The in-form Aduriz hooked a sixth-minute volley over at the near post as slack set-piece marking almost undid Barcelona.
Luis Enrique's team were far from their fluent best during the opening exchanges and required a slice of fortune to take a 14th-minute lead.
The chance was presented by a needless handball from Iker Muniain and Messi's resulting free-kick spun wickedly off the defensive wall to elude Gorka Iraizoz.
Claudio Bravo in the Barcelona goal showed superb reactions to thwart Aduriz when he prodded goalwards in the 20th minute - a save that was soon bettered by opposite number Iraizoz keeping out a Suarez header from point-blank range.
Markel Susaeta's free-kick was pushed clear by Bravo before Suarez ended a period of dominance for the goalkeepers, driving at the Athletic defence and exchanging passes with Messi to rifle a 20-yard drive that Iraizoz got a hand to but could not stop.
Barcelona should have led 3-0 in the 29th minute as Xavi sprung the offside trap to round Iraizoz but Neymar's effort from his cutback was cleared off the line by Aymeric Laporte and Suarez was unable to convert the follow-up.
Aduriz almost hauled Athletic back into the match when Gerard Pique failed to clear Mikel Balenziaga's cross and the striker nodded against the left-hand post, while Unai Lopez side-footed a volley wide when given ample room to reduce the arrears after 53 minutes.
That early second-half miss spurred Athletic on and they finally found the net as Rico tapped home on the rebound when Bravo saved from Aduriz.
Messi conceded possession in the build-up to that goal, but made amends by helping to restore Barcelona's two-goal advantage in the 62nd minute - steering Suarez's dinked cross towards goal where it struck the unfortunate De Marcos and crossed the line.
Two minutes later, Ivan Rakitic and Messi orchestrated a sublime counter-attack, the latter's pass was dummied by Xavi and Neymar stroked home a clinical finish from the edge of the area.
The goal-rush continued as Muniain caught Busquets napping to play in Aduriz for the goal his efforts deserved.
Etxeita somewhat soured a magnificent exhibition of football with his X-rated challenge, but only temporarily as Pedro - Suarez's replacement - capped victory in wonderful style.
