Madrid, which begins its Group B campaign at Galatasaray on Tuesday without injured midfielder Xabi Alonso and defender Raphael Varane, lost in the semifinals of the lucrative competition over the past three years, last season to Borussia Dortmund.
To boost its chances of renewed success, Madrid has also parted ways with former coach Jose Mourinho to hire Carlo Ancelotti, who won the European Cup twice with AC Milan.
"Real Madrid have not made it into the final of the Champions League since 2002 and that's amazing when you think about it," Ancelotti said. "I think it's been too long for a club of Madrid's stature."
Ozil is arguably the best passer in European football and by letting him leave, Ancelotti is laying the foundations for a more direct approach, one that relies less on craft and more on the explosive pace of Bale and Ronaldo
Madrid, whose other opponents in the group stage are Juventus and FC Copenhagen, was not the only major club to replace its coach during the offseason as nearly all the Champions League contenders had the same idea: Chelsea re-hired Mourinho, Manchester City signed Manuel Pellegrini, United replaced Alex Ferguson with David Moyes, Barcelona appointed Gerardo Martino and Bayern has gone for Pep Guardiola.
Bayern is still adapting to life under its new coach, but the signing of Mario Goetze from last season's finalist Borussia and the addition of Thiago Alcantara from Barcelona are likely to pay long-term dividends.
"We're a bit lethargic, we play football without emotion, we're doing the minimum," said Bayern sporting director Matthias Sammer. "That's not enough for the level of football that we want to play."
Sammer said Bayern will need to make a "different appearance" at home against Russian league leader CSKA Moscow in Group D on Tuesday with more "emotion and passion" to deliver the "last two or three percent that we're missing." Bayern's other opponents are Manchester City and Viktoria Plzen.
Looking to win its fourth Champions League in nine years, Barcelona will also be trying to get its unofficial title of best team in the world back after being thrashed by Bayern in the semifinals last season. The club has been placed in a difficult Group H with Ajax, Celtic and Milan.
"There's (...) a bitter taste after what happened in the semifinal against Bayern Munich, where there was a big gap between the two teams - we didn't go into it in our best shape. But that's the past and we have to look forward," Barcelona's Lionel Messi said.
Barcelona and Atletico Madrid are the only two teams in Spain to have a perfect start to the league season with four wins in as many rounds. Messi has been the driving force behind his team's start with a league-leading six goals in just three appearances. New signing Neymar is fitting in with two assisted goals for Messi already.
Manchester United, playing in the Champions League without Ferguson for the first time, will start its campaign in a group containing Bayer Leverkusen Real Sociedad and Shakhtar. According to Moyes, Ferguson told him to brace himself for a difficult group phase.
"He said he thinks it's one of the hardest draws United have ever had in the Champions League," Moyes said ahead of Tuesday's home match against Leverkusen. "If that's coming from him, it must be tough."
Chelsea is in Group E with Basel, Schalke and Steaua Bucharest.
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AP Sports Writer Jerome Pugmire and Associated Press writers Ciaran Fahey and Joe Wilson contributed to this report