Juventus claimed a 1-0 win over Manchester United at Old Trafford while English champions Manchester City thrashed Shakhtar Donesk 3-0 in Champions League action.
Paulo Dybala's 17th-minute goal, a simple conversion after a low cross from the right by former United favourite Cristiano Ronaldo, proved decisive but the Italian champions could have returned home with a much more convincing margin.
United's Spanish keeper David De Gea made a series of good saves including an excellent effort to keep out a second-half strike from Ronaldo.
Paul Pogba struck the post with a left-foot effort from outside the box in the 75th minute but Jose Mourinho's side struggled to create openings against a superb Juve defence.
First-half goals from David Silva and Aymeric Laporte were added to by substitute Bernardo Silva as Pep Guardiola's City won easily in Group F.
City have now won six of the seven games they have played since losing 2-1 to Lyon in their last Champions League outing.
In Spain, hosts Real Madrid beat Plzen 2-1 thanks to a headed goal from Karim Benzema (11th) and a cool finish from Marcelo Vieira in the 55th minute.
But the Czechs fought back with a goal from Patrik Hrosovsky in the 78th minute to give local fans a few nervy moments at the Bernabeu.
Real held on for a far-from convincing win which takes them joint top of Group G with AS Roma on six points after three games
Bayern Munich scored twice in two minutes to beat hosts AEK Athens 2-0 to climb to the top of their Champions League Group E.
Javi Martinez volleyed in after 61 minutes and Robert Lewandowski tapped in their second goal two minutes later for their second win in three group matches.
In Bern, Champions League debutants Young Boys scored their first goal and picked up their first ever point in the competition with a deserved 1-1 draw at home to Valencia.
Michy Batshuayi gave Valencia a first-half lead but Guillaume Hoarau equalised with a penalty after the break.
In other matches Roma thrashed CSKA Moscow 3-0, Ajax beat Benfica 1-0 with a goal from Noussair Mazraoui in added time while Hoffenheim drew 3-3 with visiting Lyon.