Keown acknowledged that while Los Rojiblancos are a good side, Mourinho will think that he has been given a favourable draw with Real Madrid playing Bayern Munich in the other tie.
He told the Daily Mail: "I think they've been quite lucky with the draws.
"Atletico Madrid have had a fantastic season but they might now start to think about what they are achieving and they could wobble. Mourinho will be pinching himself that he is playing Atletico in the semi-finals of the Champions League.
"They are a much improved side but they are not Bayern Munich or Real Madrid and Mourinho will think he has the necessary tactical plan to overcome Diego Simeone."
Chelsea host Sunderland on Saturday.