Liverpool were the favourites to win in the Spanish capital, but Atleti put in a famous defensive display to topple Jurgen Klopp’s men.
Simeone’s side scored early on through Saul Niguez, and then soaked up a huge amount of Liverpool pressure throughout the match.
It was an impressive defensive display from Atletico, as they put themselves ahead in the tie.
But Simeone claims that he still thinks Liverpool are the toughest team to play against in world football.
“When you work as a team, in a block, you can do whatever you want. It's not the best party ever because we didn't win a trophy,” Simeone said.
”Don’t forget. The best team in the world came here, and we beat it.”
Liverpool actually were limited in the chances that they created against Atleti, despite having much of the ball.
Mo Salah had two openings and Jordan Henderson also went close, but outside of those two opportunities, Liverpool struggled to create much else.
Atleti still have it all to do to qualify from the tie though, as getting a positive result at Anfield in the second-leg will still remain a very difficult challenge.
Have something to tell us about this article?