Mikel Oyarzabal's second-half penalty secured a 1-0 victory over Athletic on Saturday in what was the first ever final between the two great rivals in their current guises.
The rescheduled 2020 decider was played 350 days later than initially planned in Seville due to the coronavirus pandemic.
Oyarzabal settled the first all-Basque Copa del Rey showpiece since 1927 on an emotional night for head coach Imanol and La Real.
Might be the best pressconference performance from a coach I ever seen!— Alexandra Jonson (@AlexandraJonson) April 3, 2021
"As a manager, you can imagine I am very proud," Imanol told reporters. "I have a great feeling.
"This week, my uncle died from COVID. We received so many messages during these two weeks from all over Gipuzcoa.
"The suffering of my family, there are so many things. When I left yesterday, I was crying after receiving a video from my family members.
"There so many feelings. I am very happy, super proud to be the manager of this Real Sociedad that have made history, as we said yesterday.
"It would not have been possible without the support of the fans. Thanks to everybody."
"There so many emotions," he added. "I was in the third division with almost half of this squad four or five years ago fighting around the stadiums of Vizcaya.
"You can't imagine the emotion I can feel in this moment for being able to make the fans happy."
Oyarzabal has scored 89.5 per cent of his penalties taken for La Real in all competitions – only Real Madrid captain Sergio Ramos (18) among LaLiga players has scored more penalties than him since the beginning of the 2018-19 season across all competitions (17, same as Barcelona superstar Lionel Messi).
"It's an incredible day," said a tearful Oyarzabal post-match.
"You remember everybody, all the people who would have loved to be here, people who have left us. This is for everyone, my family, my friends. It means everything."
It was another case of so close but yet so far for Athletic, who finished runners-up in the Copa del Rey for the fifth consecutive time, having also fallen short in 1985, 2009, 2012 and 2015.
Athletic equalled Madrid (five from 1918 to 1933) as the team to lose most consecutive finals in the competition's history, though Marcelino's men have the opportunity to snap that streak when they face Barca in the 2021 decider on April 17.
"I am not disappointed, because I was proud of the players I coach before the game, and I continue so. But obviously I am sad," head coach Marcelino said. "Especially, because we haven't been ourselves.
"When you far for your version, this can happen, the opponent in a specific action with not much superiority, although deserved overall, they win a title. So, we have to congratulate Real [Sociedad]. We have to assess calmy what we have to improve because we have one more option in 15 days."