The Basques had claimed the scalp of Manchester United on their way to the tournament decider, but they turned in a disappointingly flat performance in Bucharest
The Basques had blazed their way into the tournament decider, sweeping Manchester United and Schalke aside with their Barcelona-esque brand of football.
However, they were completely outplayed by Atletico, which cruised to victory thanks to goals from South American duo Radamel Falcao, who struck twice, and Diego.
"I feel tremendously disappointed," Bielsa is quoted as saying by UEFA.com. "We didn't play well.
"We played how Atletico wanted us to, allowing them to play their way in the process. Obviously, I'm responsible for how my team played and we did not accomplish our goal.
"Our opponents were deserving winners. There was a stark difference between the teams."
Athletic, which finished as runner-up to Juventus in the two-legged 1978 UEFA Cup final, had been hoping to end its wait for a first major European trophy in Bucharest.