Lionel Messi gave Barca the perfect start by grabbing his 33rd goal of the season and had a hand in his team's other four goals at the San Memes stadium.
Messi's opener had a touch of fortune as it came from a deflected free-kick and he set up Luis Suarez for the Uruguay forward to double the advantage before halftime.
Athletic refused to lie down and Mikel Rico pulled a goal back on the hour mark before Messi's goalbound header was then turned into his own net by Oscar de Marcos.
The Catalan giants went 4-1 ahead when Neymar scored his 23rd of the season, Messi again with the assist.
Aritz Aduriz pulled another goal back for Athletic but the home team's hopes ended when Xabier Etxeita was shown a straight red card for a nasty challenge on Suarez before Pedro Rodriguez added a fifth.
It was the ninth straight win for Barca, who will have taken heart from seeing Real thrashed 4-0 by reigning champions Atletico Madrid Saturday.
Man Utd held
Barcelona's fellow European powerhouses Manchester United missed the opportunity to close up in the English Premier League title race when it was held 1-1 at West Ham.
The home side looked set to secure all three points after a superb piece of skill from Senegal's Cheikhou Kouyate just after half time at Upton Park.
He turned and volleyed home to put the Hammers ahead, but United kept battling and Daley Blind crashed home an equalizer in injury time.
United's Luke Shaw was then sent off for a second yellow card and the draw leaves Louis van Gaal's team in fourth spot -- one point clear of Tottenham Hotspur, whose 2-1 win over Arsenal was the highlight of Saturday's program.
In other EPL action, former England striker Peter Crouch scored a late equalizer as Stoke City drew 1-1 at Newcastle in a mid-table clash, while relegation battlers Burnley and West Bromwich Albion shared four goals.
Roma closes gap
In Serie A, AS Roma closed the gap on leaders Juventus to seven points with a 2-1 win at Cagliari.
It took a late winner from Leandro Paredes to give Rudi Garcia's men a first win after four league draws.
Napoli consolidated third place with a 3-1 home win over Udinese, while Samuel Eto'o made his debut for Sampdoria off the bench but his new team was held 1-1 by Sassuolo to stay fifth.