Atletico took charge of the round 16 tie with this first-leg 5-2 win at the Metropolitano.
Simeone said afterwards: "I liked the team; we forced their mistakes. It gave us the confidence to build a significant lead in the first half. We were able to deal with their first goal better. From 4-2, we went to 5-1 between Julián (Alvarez) and (Antoine) Griezmann, and the finish came after a 50-metre run.
"Then they scored after one of our mistakes. We'll enjoy this victory, but the Champions League is tough, and no result guarantees qualification."
On Julian Alvarez, he also said: "I see him happy, content, scoring goals. Of all the teams he's been on, this is where he's scored the most goals. He seems committed, positive, and he's back to his previous form. I'm happy for him, and I hope he can stay for many years. I hope we can build a good team so he can stay."
He continued: "The first half was better, in the second half the changes didn't work as well as usual.
"We needed to continue with the same intention as at the start. The team played a good game overall and at the beginning forced situations to make things happen. The victory could have been more decisive."