Liverpool began its Champions League title defence with a 2-0 defeat away to Napoli, which scored two late goals to decide a cagey encounter at the Stadio San Paolo on Tuesday.
Dries Mertens scored from the penalty spot with eight minutes remaining after Andy Robertson tripped Jose Callejon inside the box and Napoli substitute Fernando Llorente added a second in stoppage time to put the result beyond doubt.
Juergen Klopp’s side became the first competition winner to lose the opening game of its Champions League defence since AC Milan was defeated by Ajax Amsterdam in 1994.
Hirving Lozano headed in from close range early on but the goal was correctly ruled out for offside, before Sadio Mane forced Alex Meret into a save and Roberto Firmino flashed a header wide before the break.
Adrian denied Mertens with a superb reaction stop early in the second half before Meret dived to direct Mohamed Salah’s effort wide.
But the late double from Mertens and Llorente secured the three points for Carlo Ancelotti’s side, which also beat Liverpool at home at the same stage last season.
In the other Group E game, Salzburg made an impressive start with a 6-2 victory at home to Genk.
Erling Haaland scored a first-half hat-trick for the Austrian champion, becoming the third youngest player to net a Champions League treble at the age of 19 years and 58 days, behind Raul (18y 113d) and Wayne Rooney (18y 340d).
At London, Valencia gatecrashed Frank Lampard’s managerial bow in the Champions League by earning a morale-boosting 1-0 win at Chelsea after Ross Barkley spurned a chance to equalise by missing from the penalty spot.
Spain forward Rodrigo Moreno gave the visitor the lead against the run of play in the 74th minute of the Group H game, getting the slightest of touches on a free kick from Dani Parejo to send the ball into the roof of the net.
Chelsea continued to threaten and was awarded a penalty after a VAR review spotted a handball by Valencia defender Daniel Wass, but Barkley sent the resulting spot kick on to the crossbar and over.
Borussia Dortmund hit the woodwork and had a penalty saved before drawing 0-0 with Barcelona in its Group F opener, at Dortmund with Lionel Messi making his first appearance of the season for the Spaniards.
Barca’s in-form 16-year-old Ansu Fati became the club’s youngest player to feature in a UEFA competition when he started.
He failed to make any real impact before being replaced by fit-again Messi just before the hour mark.
The results : Napoli 2 (Mertens 82-pen, Llorente 90+2) bt Liverpool 0; Salzburg 6 (Haaland 2, 34, 45, Hwang 36, Szoboszlai 45+3, Ulmer 66) bt Genk 2 (Lucumi 40, Samatta 52); Borussia Dortmund 0 drew with Barcelona 0; Benfica 1 (Seferovic 84) lost to RB Leipzig 2 (Werner 69, 79); Chelsea 0 lost to Valencia 1 (Rodrigo 74); Ajax 3 (Promes 18, Alvarez 50, Tagliafico 62) bt Lille 0.
Inter Milan 1 (Barella 90+2) drew with Slavia Praha 1 (Olayinka 63); Lyon 1 (Depay 51-pen) drew with Zenit 1 (Azmoun 41) .
