Villarreal won 4-3, with Dani Parejo scoring in the tenth minute of injury-time.
Giraldez later said: "In the last minutes we had five resounding chances to win the game, also with players who were specialists in finishing. Today they were unlucky and I think it is a very serious mistake last goal, which is what bothers me the most, with a corner in favour and then a childish penalty, which sums up the game quite well in the last action.
"There are times when the match is for you not to win.
"We wanted to win the game. We have had moments to win it and sentence it and moments in which we have had to suffer, from lack of control, against a great team. We are building a winning team, with a champion team mentality. We are a brave team in all fields. We could have settled for a draw and we wanted to win it. I think we should have won the final game."
Giraldez also said: "We have had clear chances, two one-on-ones against the goalkeeper and we have not made the right one, something we did the other day. It is a lot of merit to come here and have the brilliant moments that we had.
"The team's reaction to the 3-2 and with the tie we want to continue going for the game.
"We have to go with our heads held high."