The 30-year-old thinks success has helped Los Rojiblancos, as well as new manager Diego Simeone, while he hailed Blues' keeper Thibaut Courtois who is on-loan at the Madrid outfit
The Blues were drawn in the same group as the Spanish outfit in the competition three seasons ago, beating them at home and drawing away as the west London side went on to progress as winners.
Atletico failed to qualify from the group, finishing in third place behind Porto, but the Czech international insisted that they are now a much-improved outfit having tasted success and will prove very tough opponents.
"I've played against Atletico before, but since Diego Simeone's arrival in the dugout their playing style has changed," the keeper told Uefa.com.
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"They're very disciplined, with an especially solid defence, and are difficult to handle on the counterattack.
"Also, because they're a Spanish team, they all want the ball and feel comfortable on it.
"With this change of style, Atletico are much more dangerous than when we faced them in the 2009-10 Champions League.
"Success has helped them. They are very well-drilled so beating them won't be easy."
The Premier League outfit qualified for the Super Cup final by winning last season's Champions League, defeating Bayern Munich on penalties in the final, whereas Atletico beat Athletic Bilbao 3-0 in the Europa League final to earn their place.
Blues keeper Thibaut Courtois was part of Los Rojiblancos' team that were victorious in Europe last year having extended a loan spell at the Madrid-based club after joining Chelsea, and was impressive for the team that finished 5th in La Liga.
Cech praised the 20-year-old keeper's attributes, suggesting he is not easy to score past, indicating that the Belgian is very mature for his age.
"He has very good self-control and great concentration for 90 minutes," Cech added. "He seems much more experienced than he is, so his great advantages are his head and mental strength.
"He can stay calm in decisive games – that's not easy at his age. He's tall, has very good reactions and is actually very quick, so it's hard to score against him."