Athletic have secured qualification to the European Cup for the first time since 1998. A 3-0 away win at Rayo Vallecano on Friday secured fourth place ahead of Sevilla and Real Sociedad.
Goals from Mikel San Jose, Oscar De Marcos and Ander Herrera gave Athletic their highest league finish in 17 years, when they finished runners-up to Barcelona in La Liga in 1997.
San Jose grabbed the first with a clever flick from a corner which couldn’t be reached by Ruben, who had sprinted off his line in his attempts to gather Susaeta's corner
Rayo were undone by another set piece just 15 minutes later, as the home side again failed to clear Susaeta’s ball in, giving De Marcos the opportunity to smash home a second.
Herrera sealed the win 15 minutes from the end with a beautiful free-kick and gave Athletic the fourth place finish they dreamt of.
"This is the result of a lot of hard work over the season but now we can enjoy this moment," San Jose told reporters.
"I was lucky enough to score the first goal that helped us to achieve our aim."
Bilboa are nine points ahead of Sevilla, having played a game more. But should Sevilla catch up, their poor head-to-head record would see them remain in fifth.
Athletic beat Sevilla 3-1 last week’s crucial match, which, in addition to their early season draw gives them a better record.
Such was the scale of the celebrations by the Basque supporters, that the fence keeping fans safely tucked away in the stands gave way as supporters collapsed onto the pitch, although no-one was seriously injured.
Manager Ernesto Valverde is pleased that his side have been able to wrap up qualification this early: "It's a huge joy, getting the opportunity to play in the Champions League.
"It's true that we were all very tense, we took the game that way, but now we're in heaven.
"For us it's a success to get into the qualifying stage of the Champions League but we've got another challenge before that and it's to get as many points as we can, adding continuity to what we're capable of doing," he added.
Bilbao are still 12 points off third place Real Madrid who have two games in hand, such is the gap between the top three and the rest of the chasing pack.
Despite the loss, Rayo fans were also in high spirits throughout the match. Overjoyed with their high league position (currently ninth), the fans threw toilet paper onto the pitch in celebration, causing the start to be delayed by 15 minutes.
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