Barcelona still have a perfect record in Group D as they beat Olympiakos 3-1 despite having Gerard Pique sent off in the first half.
Driving rain meant the mostly uncovered 99,000-capacity Camp Nou was largely empty as it opened to fans for the first time since a violent crackdown of an independence referendum in Catalonia on October 1.
Those who did turn out saw Pique stupidly collect a second yellow card for handling the ball into the net late in the first half.
Barca were already ahead at that point from a Dimitrios Nikolaou own goal and they added further goals in the second half with Lionel Messi netting a free-kick — his 100th European goal — and setting up Lucas Digne to score.
Nikolaou pulled one back for the Greeks, who are still pointless.
Juventus are second in the group after coming from behind to beat Sporting Lisbon 2-1 in Turin, with Miralem Pjanic curling in a free-kick to cancel out Alex Sandro’s own goal and Mario Mandzukic heading in a late winner.
PSG continued their superb start in Europe this season as their ‘MCN’ attack all scored in a 4-0 victory at Anderlecht.
Kylian Mbappe opened the scoring inside two minutes and Edinson Cavani headed in the second before the interval.
Neymar’s free-kick made it three in the second half, with substitute Angel di Maria completing the rout.
PSG are top of Group B with nine points, three more than Bayern Munich, who eased to a 3-0 victory over Celtic.
The 72-year-old Jupp Heynckes was back in the Bayern dugout and he saw Thomas Mueller, Joshua Kimmich and Mats Hummels all score.