Jose Mourinho admitted this season was the worst of his career after defeat in the Copa Del Rey final to Atletico Madrid left Real Madrid without a single major trophy this season.
Miranda's 99th minute winner in extra time consigned Real to a 2-1 loss in the showpiece final at the Bernabeu.
The game was an ill-tempered one with both Mourinho and Cristiano Ronaldo sent off, while a brawl broke out on the sidelines between the two sides.
Ronaldo opened the scoring for Real Madrid, before Diego Costa equalized for Atletico. Real were unlucky to not score a second, hitting the woodwork on three occasions, before Miranda struck in the first period of extra time to give Atletico their 10th Copa Del Rey title.
"I have failed this season," Mourinho told reporters after the game. "In the first season to win the cup after many years, reach the semifinal for the first time for a long time and fight until the end in the league is not a failure.
"Neither is in the second season, having won the league against the best team in the world (Barcelona) and to win it like we did. We lost in the Champions League on penalties in the semifinal and I cannot take penalties.
"The third season has been a disappointment, a failure or whatever you want to call it. When things are going well the credit goes to everyone and when things go badly it is the coach's fault.
"We've been close ... but that does not exist in football. It has been my worst season. For many it would be good, but it's bad for me because I have never not won a big title. The Super Cup is little return and when responsibility falls to a single person, you can say that I have failed this season."
Atletico manager Diego Simeone said he was speechless after the win, while admitting his side had that bit of luck, so vital to win a final.
"It was an incredible game," he said. "We had the luck needed to win the trophy. What these players have been doing for the past year-and-a-half is incredible.
"They finally lost their fear and the hearts of each player combined to win the match, and it was amazing. We were fortunate because in football, teams that win have a slice of luck. We believed that we'd win the game.
"What brought us these achievements has been this -- you see Diego Costa running 50 metres back, see Koke, (Radamel) Falcao and Gabi all sacrificing themselves for the team.
"I'm speechless. Now we have to think about the next game if we want to keep on developing. That's the only way we know."
