Dries Mertens and Fernando Llorente struck late to earn Napoli a 2-0 win at home to holders Liverpool in the first game of the Reds' Champions League defence.
Carlo Ancelotti's men won the corresponding fixture last term with Mertens' spot-kick and Llorente's injury-time goal enough to ensure history was repeated in the Group E clash at the Stadio San Paolo on Tuesday.
Andy Robertson was deemed to have tripped Jose Callejon in the box and, after VAR ratified the penalty decision, Mertens squeezed his penalty past Adrian in the 82nd minute.
Liverpool rode their luck in reaching the knockout rounds in 2018-19 and Jurgen Klopp's men will again have to bounce back from an away loss to Napoli this year after Llorente's first goal for the club sealed all three points.
Napoli had an early strike ruled out for offside when Hirving Lozano headed home the rebound after Adrian's excellent double save from Fabian Ruiz.
Sadio Mane's shot was saved by Alex Meret in the 20th minute - Liverpool recording their first shot on target in the game having failed to manage any in last season's visit.
And the Reds should have gone into the break 1-0 up, Firmino heading wide a fine James Milner cross on the Brazil forward's 200th Liverpool appearance.
Napoli had the first big chance of the second half, Adrian showing superb reactions to prevent Mertens from turning in Fabian's deep cross, then Mane overhit a pass to Mohamed Salah as Liverpool broke at speed.
Liverpool were starting to build pressure and, after successive errors from Kalidou Koulibaly and Kostas Manolas handed him a sight of goal in the 65th minute, Salah's drive was turned around the post by Meret.
Napoli's goalkeeper had to deny Mane again as Liverpool looked to finish strongly, but when Callejon jinked into the box he went over Robertson's outstretched leg to win a penalty.
Mertens had to wait for the VAR check, but calmly drilled his strike past Adrian, with Virgil van Dijk's terrible error in stoppage time ensuring former Tottenham striker Llorente could ease home a second.
What does it mean? History repeated in Naples
Lorenzo Insigne's late strike earned Carlo Ancelotti's side a 1-0 victory against Liverpool last season and lightning struck twice, with Liverpool becoming the first holders to lose the first game of their Champions League defence since AC Milan did so in 1994-95
Liverpool have kept only one clean sheet in eight competitive games this season, which must worry Klopp, especially as reliable leader Van Dijk was badly at fault for Llorente's clincher.
Mertens the matchwinner
An 11th Champions League goal from Mertens set up this win, with the Belgium international also helping to force Van Dijk's error for Napoli's second goal.
Ancelotti named four attackers in his starting XI with the three-time Champions League winning coach's bold selection justified by an eye-catching win.
Another away blank for Salah
Chances were at a premium for both sides for most of the game, but Salah is a player expected to create opportunities for himself. He failed to do so against a tough defence, although Mane undoubtedly should have set him up.
The Egypt star has now failed to score in all three away appearances for Liverpool this season.
Key Opta Facts:
- Napoli have now won five of their six Champions League home games against English opposition (L1 – a 4-2 defeat to Man City in November 2017).
- Liverpool have lost their opening Champions League match of a new campaign for only the second time (P12 W6 D4 L2), and for the first time since a 2-0 defeat to Valencia in September 2002.
- The Reds have lost six of their last eight away games in the Champions League (W2), as many as in their previous 25 such matches in the competition.
- Napoli striker Dries Mertens has scored more Champions league goals than any other Belgian in the competition (11).
- Since a 2-0 win over Udinese as Borussia Dortmund boss, Liverpool manager Jurgen Klopp has lost on his last five visits to Italian sides in all competitions (P5 W0 D0 L5).
- Napoli striker Fernando Llorente has now scored a Champions League goal for four different clubs (Juventus, Sevilla, Spurs and Napoli) – the joint-most sides of all Spaniards alongside Fernando Morientes.
Liverpool travel to Chelsea in a blockbuster Premier League clash on Sunday, the same day Napoli go to Lecce in Serie A. When the Champions League returns for matchweek two early next month, Anfield will welcome early group leaders Salzburg with Napoli going away to Genk.