Barca were 4-2 up in the first-leg of the Copa semi, only for Atletico to fight back for the 4-4 draw at Montjuic.
Martinez said afterwards: "The game could have been 6-2 and it ended 4-4. We were superior throughout but when you give Atlético chances you see that they are capable of scoring goals. The last stretch was not good at all: we lost possession and gave away goals. In the end, we leave with a bittersweet feeling.
"It's true that we could have kept our line a little further back in that action, but that doesn't mean we're leaving with this draw. We were superior. We have to know how to handle the final moments of the game better. We had the fifth and we didn't know how to score. And doubts begin to appear. They took advantage of the four they had."
He added, "The start wasn't good at all. We came out a bit sleepy. Then we showed our level and did the hardest part, which was getting ahead. The last stretch was what hurt us the most. It can't happen again, especially in a knockout round. Everything is still open and it will be a tough match there, but we showed that we are far superior, although if we make mistakes, we will pay dearly."