Carlo Ancelotti admits Chelsea have not been at their best in the Champions League despite a 100% record in the competition so far.
Chelsea are top of Group D having won both their opening games against Porto and Apoel Nicosia. Nicolas Anelka scored the decisive goal in both 1-0 victories but the performances were far from convincing.
"We have had difficult games in the Champions League," said Ancelotti. "Porto, in the first game, was not an easy match because they have very good organisation."
He added: "The same thing against Apoel Nicosia. Everyone thinks that playing in Cyprus is easy, but it's not. Football in Cyprus has improved. For example, the national team won 4-1 against Bulgaria recently.
"There are no easy games. We can play better in the Champions League, for sure, but at the moment it's important to win.
"We want to play our best in March and April when the matches are very, very important.
"Atletico have not started the season well, but they have a very good quality.
"In attack they have Sergio Aguero and Diego Forlan who are dangerous strikers. We have to pay attention to this.
"Aguero has fantastic quality and he can resolve the match with his quality. They're a good team but, at this moment, they haven't found a good disposition tactically on the pitch.
"I think that Atletico has a possibility to return to playing well because they have a lot of quality. Now, at this moment, for them it's not easy because Porto have also made a good start."