The 2010 champions Atletico have won 11 successive matches to reach the final while fearless Athletic, who only field players of Basque origin, have lit up the competition under eccentric Argentine coach Marcelo Bielsa with their possession-based style that has drawn comparisons with Barca.
Athletic made the rest of Europe take notice when they beat Manchester United home and away in the last 16, then accounted for Schalke in the quarter-finals with an attacking intensity that the Bundesliga side, like United before them, could not handle.
Powerful centre forward Fernando Llorente's physical presence is sure to cause problems for an Atletico defence that is vulnerable in the air, particularly at set pieces, while versatile attacking midfielder Iker Muniain, only 19 and attracting the attention of bigger clubs, pulls the strings.
If Atletico pay too much attention to Muniain and Llorente, then they risk being punished by the equally talented Ibai Gomez, Markel Susaeta and Javi Martinez.
"We will try to play naturally, with a lack of inhibition, because this will bring us closer to a victory," said Bielsa, who took the helm at the north-coast club at the beginning of the season.
"Throughout every game, regardless of their importance, I haven't seen a problem with confidence or anxiety yet that the team were not able to resolve themselves."
Atletico, who have improved steadily under their former player and Argentina captain Diego Simeone since he took over in December, also boast a potent strike force in summer signings Adrian Lopez and Colombian Radamel Falcao, who hit the winner for Porto in last year's final.
After comfortably winning their group following a journey that began in the third qualifying round back in July, Atletico under Simeone have knocked out Lazio, Besiktas, Hanover and La Liga rivals Valencia.
Simeone's side will try to match Athletic for intensity and not allow their opponents time on the ball.
Gabi is likely to replace the suspended Tiago, sent off in the second leg against Valencia, alongside Mario Suarez in central midfield.
"The sides are very evenly matched. I haven't spoken to Bielsa but I have a great admiration for him," Simeone said.
"It's an important event for everyone. A moment of great pride. Atletico are a cup team and another final is something for the fans to enjoy."
Simeone and Bielsa know each other well, with Simeone playing the last 30 of his 106 international appearances during Bielsa's six-year run at the helm between 1998 and 2004.
Bielsa said he had not spoken directly to Simeone, only through his opposite number's assistant, another Argentine he knows well, former international goalkeeper German Burgos.
"We have agreed not to speak until a month after the final. Burgos acts as the intermediary," Bielsa said.
"I want to win the final, regardless of whether two players I used to coach are in the other dugout or not."
Athletic have never won a European trophy, their only previous final coming in 1977 when they lost the UEFA Cup showpiece match to Juventus.
Each side has a win apiece in their clashes in La Liga this season. Llorente scored twice in a 3-0 home win for Athletic in October but Falcao's double secured Atletico a 2-1 victory at their Calderon home in March.
The last time two Spanish teams contested the final of the competition, formerly known as the UEFA Cup, was in 2007 when Sevilla beat Espanyol on penalties after a 2-2 draw.
Athletic Bilbao: 1-Gorka Iraizoz, 15-Andoni Iraola, 5-Fernando Amorebieta, 3-Jon Aurtenetxe, 24-Javi Martinez, 14-Markel Susaeta, 8-Ander Iturraspe, 21-Ander Herrera, 19-Iker Muniain, 9-Fernando Llorente, 28-Ibai Gomez
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