Liverpool, Champions League runners-up last season, suffered a shock 4-1 defeat to Napoli in their opening Group A game at the Diego Armando Maradona Stadium on Thursday (NZ time).
Napoli were quick out of the blocks with Victor Osimhen hitting the post in the second minute and then three minutes later they grabbed the lead when James Milner handled in the box and Piotr Zielinkski converted the penalty.
Napoli were opening up Liverpool with ease and were awarded a second penalty but Alisson Becker saved from Osimhen only for the home side to grab a two goal advantage shortly after thanks to a cool finish from Andre-Frank Zambo Anguissa.
Substitute Giovanni Simeone made it 3-0 just before the break, slotting home after the outstanding Khvicha Kvaratskhelia had beaten Trent Alexander-Arnold and Joe Gomez and slipped the ball across.
Liverpool replaced Gomez with Joel Matip at the break but within two minutes of the restart Napoli went 4-0 up as Zielinksi saw his shot blocked by Alisson but reacted sharply to poke the ball home.
Juergen Klopp's side pulled a goal back two minutes later thanks to a fine curling shot from Luis Diaz but there was no way back for the English side.
Richarlison's first goals for Tottenham Hotspur helped them mark their return to the Champions League with a 2-0 victory over 10-man Olympique Marseille in Group D.
The Brazilian forward, signed from Everton in the summer, struck twice in five minutes late on to secure three points that had not looked likely for the hosts.
Richarlison rose to head home Ivan Perisic's pinpoint cross in the 76th minute and scored an almost identical goal from Pierre-Emile Hojberg's cross to deflate Marseille.
Until Richarlison's brace Tottenham had been mediocre against a lively Marseille who were the better team until Chancel Mbemba was sent off three minutes into the second half.
Tottenham, who missed out on the Champions league for the past two seasons, did not register a shot on target in a lacklustre first half but Richarlison eventually ensured a perfect start for Antonio Conte's team.
They share top spot in the group with Sporting Lisbon who beat Eintracht Frankfurt 3-0.
Bayern Munich's Leroy Sane scored one goal and forced an own goal by Inter Milan as they beat the Italian side 2-0 away in their Group C opener.
Germany international Sane superbly controlled a pinpoint Joshua Kimmich cross before rounding Inter keeper Andre Onana, who was making his debut for the club, to give Bayern the lead in the 25th minute.
Sane also deserves a lot of credit for their second goal after dismantling the Inter defence with a lightning-quick double one-two with Kingsley Coman in the 66th before his shot was turned into the net by Inter captain Danilo D'Ambrosio.
Bayern, who bounced back following two consecutive draws in the Bundesliga, host Barcelona next week, while Inter, who have now lost their last two matches following their derby loss to AC Milan on Saturday, take on Viktoria Plzen in the other group match.
In other results, Barcelona crushed Vikotria Plzen 5-1, Atletico Madrid edged Porto 2-1 and Ajax dispatched Rangers 4-0.
Reuters
