Lionel Messi bagged a hat-trick to go with goals from Neymar, the evergreen Andres Iniesta and a Luis Suarez double.
Bayern Munich were also big winners on the night as they thumped Russian side FC Rostov 5-0. Robert Lewandowski scored a penalty, while Thomas Muller, Juan Bernat and Joshua Kimmich (two) also found the back of the net.
Last year’s runners up Atletico Madrid rode their luck to defeat PSV Eindhoven thanks to a first half goal from Saul.
PSV missed a penalty, had a goal dubiously disallowed and had two more strong shouts for a spot-kick.
Arsenal fought back for a point after going behind to Paris St Germain inside 43 seconds as Edison Cavani netted. Alexis Sanchez equalised 12 minutes from time.
Polish striker Arkadiusz Milik scored twice as Napoli won 2-1 at Dynamo Kiev.
Benfica and Besiktas played to a 1-1 draw, while Swiss side Basel also had to settle for a draw at home to Ludogorets.