Real Madrid's Cristiano Ronaldo (C) celebrates a goal with team mate Gareth Bale against Galatasaray during their Champions League Group B soccer match at Turk Telekom Arena in Istanbul Sept 17, 2013. [Photo/Agencies]

Ronaldo's former Manchester United team mate Wayne Rooney also scored twice in the English champions' 4-2 victory over Bayer Leverkusen as the Old Trafford club began their first European venture without Alex Ferguson at the helm since 1985.

Ferguson, who twice steered United to Champions League success, watched as Rooney's double and goals from Robin Van Persie and Antonio Valencia gave new boss David Moyes a pleasing, if sometimes anxious, first taste of the group stage.

Edinson Cavani was on target for big-spending Paris St Germain as the French club began with a 4-1 win at Olympiakos Piraeus in Group C. Twice former European Cup winners Benfica matched them with a 2-0 win at home to Anderlecht.

Not all the European aristocrats had it their own way, however, with Juventus held to a 1-1 draw at FC Copenhagen.

Bayern Munich's main Group D rivals look like being Manchester City with the English Premier League club easing to a 3-0 win away to Czech side Viktoria Plzen.

Edin Dzeko, Yaya Toure and Sergio Aguero were on target after the break for City who are aiming for the knockout rounds for the first time after missing out in the last two seasons.

Real Sociedad's return to the Champions League group stage for the first time since 2003-04 went flat as Shakhtar Donetsk returned from Spain with a 2-0 victory in Group A.