The Portuguese did not hesitate to write off the campaign as the least successful of his reign in Spain but insisted Atletico Madrid was "lucky" to have triumphed.
Joao Miranda's extra-time header compounded Madrid to defeat on home turf on Friday, and signaled the Mourinho's first campaign without a major trophy in over a decade - barring a Supercopa success over Barcelona back in August.
Speaking after the game, the 50-year-old admitted the season was a blot on his CV when placed in the context of his own high standards.
"This was the worst season of my career. For many coaches it would be a good season, but for me it is the worst," Mourinho told reporters. "I always showed up in the press room every time we drew or we lost. This year's campaign was a failure but my first two seasons were successful."
Mourinho's future has been shrouded in speculation for some weeks now as rumors of a return to the Premier League with Chelsea gather pace, but he insisted he has yet to discuss his future with president Florentino Perez.
"I have a contract that is valid for three more year," he said. "I still haven't talked to the president about my future."
Mourinho - who was sent to the stands midway through the second half at the Santiago Bernabeu - then claimed in his post-match assessment that Atletico was "lucky" to lift the trophy after his side hit the woodwork three times and was foiled by a number of stunning saves from Thibaut Courtois.
"I don't think Atletico deserve to be champions but they won the title. We had two clear chances on goal, we hit the post three times. This is why I think it is unfair," he added. "Atletico's keeper was fantastic but he was also lucky tonight."