Athletic Bilbao coach Ernesto Valverde said their Supercopa de Espana triumph was more nerve-rattling than the scoreline suggested.

The Basque club downed Barcelona 5-1 on aggregate, after earning a 1-1 draw at Camp Nou on Monday to end a 31-year title drought.

Barcelona looked to bounce back from losing the first leg 4-0 when Lionel Messi scored just prior to half-time, but that is where the European champions' comeback ended - with first-leg hero Aritz Aduriz forcing a draw on the night with a 74th-minute goal.

"The first half was very hard because they are great and tightened the screws after the first goal," Valverde said via AS. 

"We have come up in the second half have been very good and we have achieved the goal... you can think outside it was not too bad, but when we allowed the goal, we trembled."

Valverde dedicated the trophy to the club's fans, many of which made the 600-kilometre-plus trip south east for the momentous occasion.

"We finally achieved the title that these people deserved," he added. "Everything is what we saw in the cup final when we came to Camp Nou to play a final and see how our people came up here know what drag and what the Athletic. We know what this means for them.

"The most important of my team is solidarity and that [we] will never let you down. It is a requirement that we Athletic sometimes we do better or worse, but we know that we will roll forward."