Manchester United made a winning return to the UEFA Champions League as they cruised to a 3-0 wn over Basel at Old Trafford.
Marouane Fellaini, who replaced the injured Paul Pogba, opened the scoring with a towering header in the 35th minute.
Romelu Lukaku doubled United's lead in the 53rd minute, before Marcus Rashford sealed the win in the 84th minute.
Chelsea were in a ruthless mood, as they thumped Dino Ndlovu's Qarabag 6-0 at Stamford Bridge.
Pedro and Davide Zappacosta gifted the Blues a two-goal lead inside the opening 30 minutes.
Cesar Azpilicueta got Chelsea's third goal in the 55th minute, before a brace from Michy Batshuayi and a solitary strike from Tiemoue Bakayoko rounded off a big win.
Barcelona made light work of Juventus at the Nou Camp, with Lionel Messi's brace taking the Argentine superstar's European goal tally to 100.
Messi also created another, finished off by Ivan Rakitic, as Barca got off to the perfect start in the European Cup.
Paris Saint-Germain showed Celtic no mercy as they romped to a 5-0 win at Celtic Park.
Edinson Cavani netted a brace, while Neymar, Kylian Mbappe and an own goal from Mikael Lustig secured the win for the French giants.
Goals from Robert Lewandowski, Thiago Alcantara and Joshua Kimmich saw Bayern Munich defeat Anderlecht 3-0 at the Allianz Arena.
Olympiakos 2-3 Sporting Lisbon
AS Roma 0-0 Atletico Madrid
Benfica 1-2 CSKA Moscow