An incredible start to the final saw Ander Barrenetxea loop a header past a labouring Juan Musso after just 14 seconds, before Atlético’s players had even touched the ball.
It was the fourth time in Rojiblancos’ six CdR games that a goal had been scored before the 20th minute this season.
Regaining some composure, Unai Marrero was equal to Julián Alvarez’s vicious direct free-kick just a few minutes later, as Diego Simeone’s side attempted to recover from the shock of conceding so early.
Marcos Llorente and Antoine Griezmann began to dictate the tempo, and the pressure soon paid off when Ademola Lookman made space for himself in the area.
Despite the close attention of three Sociedad defenders, he still managed to find the bottom corner of Marrero’s net with a low drive.
The attacks began to swing from end to end in what was an open and exciting encounter, as Gonçalo Guedes flashed a shot a whisker wide for La Real.
The remainder of the half turned into a more physical encounter, with neither side carving out any genuine goalscoring opportunities until Musso cleared out Guedes in mid-air.
This allowed Mikel Oyarzabal to send the keeper the wrong way and restore Sociedad’s lead in first-half stoppage time.
Both sides came out after the break with renewed purpose, with Atleti keen to involve Lookman as much as possible.
The early second-half momentum was certainly with Los Colchoneros, and they were still in the ascendancy at the hour mark, albeit without truly threatening.
Despite Alvarez and Griezmann having dovetailed brilliantly, Diego Simeone took off the Frenchman to freshen up his front line with 20 minutes to play.
Sociedad’s attempts to get upfield through Guedes and Carlos Soler only succeeded in putting more pressure on their defence, as the ball was quickly and consistently won back by opponents that were pushing hard for their second equaliser of the match.
As the clock ticked towards full time, La Real began to push forward but were hit by a sucker punch when Alvarez intelligently moved into space before arrowing home a left-footed laser.
Álex Baena then missed an open goal from four yards out as Atlético went hunting for a late winner.
Gaps began to develop during extra time as players tired, with the closest either side came in the first period being when Alvarez smashed the ball against the crossbar.
A disjointed last 15 minutes of play were probably to be expected, and therefore, penalty kicks would be required to decide the winner.
Alexander Sørloth and Alvarez each saw penalties saved by Marrero with Atleti’s first two kicks, ultimately sealing their fate as Pablo Marín netted the crucial kick for Sociedad.
Although Atlético were unbeaten across the last nine H2Hs (W6, D3), Sociedad have now won four of the last five meetings in this competition, continuing their cup hoodoo over the Rojiblancos with this win.
As a result, Atleti have now lost six out of their last seven games in all competitions, which will give UEFA Champions League semi-final opponents Arsenal some much-needed encouragement.
Flashscore Man of the Match: Marcos Llorente (Atlético Madrid)