Unusually in Europe, Bilbao - who face Atletico Madrid in Wednesday's Europa League final - shun expensive signings and field only players with connections to the Basque region, raising most of their own talent.
Bielsa, who took over at the start of this season, revamped the team and replaced their traditional physical style with an adventurous passing game, has earned praise for leading them to their first European final for 35 years.
However, the former Argentina and Chile coach, whose side upset Manchester United and Schalke 04 on the way, preferred to pass it on to the club's youth team coaches.
"In institutions such as Athletic, what happens in the present is always articulated and connected to what happened before, because it's an organisation which feeds off itself, which generates in its formative divisions the players who will compete and represent it in the years to come," he said.
"Obviously, whoever has taken on and developed this task in the last decade has done the job very well.
"It's up to us in this case to make use of what they have produced, this team is a young generation with a very high percentage produced in the same institution."
Bielsa, gazing constantly downwards in his usual manner, was at his philosophical best as he talked about the final.
"In relation to me and all those who are involved in a final, the emotions and feelings multiply themselves and it is up to you to transfer those particularities to which I refer into the game itself," he said.
"A league is a series of successive commitments where you always have the option of correction and change.
"A final, as the name makes clear, is single and irreversible and this condition establishes the most significant difference.
"Everything which happens will be final and unmodifiable and those of us who compete all know that this adds a very special ingredient."
He was equally verbose after being asked whether Athletic had surpassed the expectations he had when he took over.
"In a league competition, we set the target of equalling what we had achieved the year before.
"In a cup, it is impossible to establish such an objective because you have to do this on the basis of the path which has to be trodden and this is impossible to do when that path has not yet been developed."
Former Real Zaragoza midfielder Ander Herrera - one of the club’s few big-money signings - said the victory over Manchester United in the round of 16, when Athletic won both legs, was the key in the campaign.
"It was the moment we realised we could go far in this competition," he said. "We realised the team's capabilities and qualities and felt that we could beat anyone.
"We beat one of the best teams in the world and played better than them and that was a good springboard."