"I always like to think positively and I think it's a good opportunity to keep improving," Simeone told Movistar Plus.
"We had been doing a very good job, today we didn't play the game we expected, but we have to keep going.
"We played badly. We have to accept that. We didn't play well, the substitutions didn't give us the spark that they gave us at other times. We played badly, they were better and we have to accept that."
Atletico, who spent big in the summer transfer market on blockbuster signings like Julian Alvarez and Conor Gallagher, finished the match with no shots on target.
Benfica could easily have won by a bigger margin if it were not for a string of saves from Atletico goalkeeper Jan Oblak throughout the game.
Simeone offered no excuses for their performance and praised their opponents for outplaying them.
"There was no lack of tension, attitude or desire to run, we just played badly and when you play badly you are exposed to losses like this," Simeone said.
"We had been doing a very good job and today the game that you don't want to see appeared.
"Some nights are not good and we have to accept them and try to learn from what we had to go through today and recover energy for Sunday's LaLiga game (at Real Sociedad)."
