Robert Lewandowski got the Catalans off to the perfect start, beating Unai Simon with a low drive from the left side of the box in the fourth minute.
After dominating much of the first half, Barca doubled their advantage on the stroke of half-time after Ferran Torres latched on to a lovely Lamine Yamal cross before powering the ball past Simon.
The home side got off to a strong start after the break too, Fermin Lopez played a deft one-two with Eric Garcia before slotting the ball home to make it 3-0 in the 48th minute.
Things went from bad to worse for Athletic Club six minutes later when Oihan Sancet was shown a straight red card for a horrible challenge on Lopez.
Barcelona secured the points and rounded out the scoring late on with Torres adding his second of the game in the 90th minute.
Elsewhere in LaLiga on Saturday, Real Sociedad prevailed 3-1 over 10-man Osasuna at Estadio El Sadar.
The home side dominated proceedings in the first half and grabbed the lead in the 42nd minute via an Alejandro Catena strike.
However, it was a completely different story after the break, with Real Sociedad quickly levelling the scores through Brais Mendez in the 53rd minute.
The visitors took the lead six minutes later with Goncalo Guedes grabbing the goal and doubled their advantage in the 82nd minute when Ander Barrenetxea made it 3-1.
Any hopes of an Osasuna fightback were dashed when Inigo Arguibide was sent off for a foul in the 87th minute.
Villarreal took an early lead against Mallorca through Gerard Moreno in the sixth minute at Estadio de La Ceramica but Samu Costa had the visitors back on level terms within two minutes.
It was a tense affair thereafter before Tani Oluwaseyi bagged a late winner for the home side.
An Iago Aspas penalty in the 55th minute was enough to secure a narrow 1-0 win for Celta over Alaves at Estadio de Mendizorroza.
Dani Olmo is set to take centre stage as Barcelona prepare for their long-awaited return to the rebuilt Spotify Camp Nou on Saturday, with Hansi Flick confirming that the Spain international will play a key role in a midfield reshuffle.
Barcelona have been left with an unexpected selection problem after Marcus Rashford missed a second consecutive training session ahead of Saturday's La Liga meeting with Athletic Club at Camp Nou.
Barcelona's challenging 2025-26 season has been hit by yet another injury blow, with promising Barca Atletic defender Landry Farre ruled out for between three and four months due to a lateral collateral ligament injury in his right knee.
Barcelona will return to Camp Nou this weekend after more than two years away, the club confirmed.
