Atletico won 5-0 at the El Sadar on Wednesday night.
Simeone said of Felix, "He is a decisive player. Very dynamic. In that area where he occupies it's the spot to score goals.
"The second goal is a great assist from (Diego) Costa. The team's performance makes me happy. (Marcos) Llorente entered and made a tremendous contribution.
"(Alvaro) Morata was also very good and that generates something important for what is to come."
He also added of Felix: "I always expect the best from my footballers. He is working well, he came from a stage that could not finish the preseason and he has talent, when he is in the vicinity of the area he is very difficult to control.
"He took advantage of the first goal very well, was well positioned in the second."