Real won the first-leg of their round of 16 tie 2-1, with Rodrygo Goes and Brahim Diaz's goals sandwiching Julian Alvarez's effort for Atletico.
Simeone said afterwards: “I leave with the feeling that we competed well. We could have done more in terms of the goals we conceded. We must continue with this rhythm for the second leg, which will be tough and difficult, and in which we will have the support of our fans. It will be an important game.
“It is always a boost to play at home. Our people push us, give us energy. We are going to focus on Sunday (against Getafe) and, when it's time, on Wednesday we will need our people.
“We failed to take better advantage when we had control of the game. They have improved a lot by having Vinícius Júnior and Mbappé dropping back with the team, because it allows them to generate quick counterattacks.
“The best thing about the match was the reaction we had to their early goal. The team committed to the game we wanted to play. We found the goal from Julián and we ended the first half with the feeling that we were doing well."