Liverpool will accept history repeating itself should another late defeat at Napoli ultimately end in another Champions League triumph but this was a troubling start to the defence of number six for Jürgen Klopp. His European champions were vastly improved on the game they played here last season and on top when José Callejón darted into their penalty area in the closing stages. Carelessness at both ends of the pitch, and from VAR, combined to inflict familiar pain.

Andy Robertson was adjudged to have fouled Callejón and Dries Mertens converted the resulting penalty through the despairing grasp of Adrián. It certainly looked a foul to the naked eye – and to the two belonging to German referee Felix Brych – with the Liverpool left-back hanging out a leg into the run of the Napoli midfielder. And it certainly looked a dive by Callejón on review. VAR decreed otherwise. Not a clear and obvious error, apparently. “The game-changer,” said Klopp. In the desperate push for an equaliser Virgil van Dijk played a hasty back-pass straight to Fernando Llorente and the former Tottenham striker sealed Liverpool’s fate by prodding home his first Napoli goal.

Klopp had every right to lament the VAR rule book but the late defensive lapses and the failure to capitalise on several excellent openings also stymied Liverpool’s improvement in Naples. They were here with a point to prove having produced the worst performance of their campaign here last October. That was the first of three away defeats in the group stage and the Champions League still made its way back to Anfield so there will be no hand-wringing over this setback. Once again, however, Carlo Ancelotti and Napoli served up a frustrating night.

Ancelotti outfoxed Liverpool last season with two “No 6s” and a central defender, Nikola Maksimovic, at right-back. This time the coach who has won and lost Champions League finals against Liverpool opted for a more offensive approach, with Hirving Lozano partnering Mertens up front and his captain, Lorenzo Insigne, the match-winner at San Paolo last season, targeting Trent Alexander-Arnold down the Napoli left. It made for an open and highly entertaining contest between two teams willing to commit forward in numbers at the earliest opportunity. That it remained goalless so long stemmed in no small part to the quality of the four central defenders on display.

Kalidou Koulibaly is to Napoli what Van Dijk is to Liverpool and the hosts’ defensive rock was the game’s dominant force in the first half as he halted dangerous raids from Roberto Firmino and Mohamed Salah. The timing and power of his challenges brought regular roars of approval from the home crowd. With Fabinho equally impressive in central midfield Liverpool frequently created space in which their front three usually wreak havoc. Koulibaly, Kostas Manolas and their fellow defenders were having none of it, however, and Alex Meret had only one save to make from Sadio Mané before the break.

Adrián, making his Champions League debut at the age of 32, had earlier produced a fine double save to deny Fabián Ruiz. The Liverpool keeper parried the midfielder’s powerful shot at full stretch and repeated the trick when the rebound gave Fabián a second bite. Lozano headed home from Adrián’s second save but was clearly offside and his celebrations were correctly short-lived.

The game continued to flow both ways. James Milner skied over after Salah had escaped Koulibaly’s attentions for the first time and teed up the midfielder on the edge of the area. Milner almost returned the favour when Liverpool broke dangerously through Jordan Henderson and Mané but, with Salah lurking unmarked at the back post, his low cross was cut out by the sliding Mário Rui. Firmino headed the subsequent corner from Salah just wide.

Neapolitan heads were in hands early in the second half after Adrián produced a stunning save to prevent Mertens making the breakthrough. Liverpool were prised open when Insigne released Mário Rui down the left – Alexander-Arnold received little protection all night – and the home full-back floated a delightful cross to the back post that evaded Van Dijk and Mertens met with a flying volley. The Belgium international was imagining his goal celebration when Adrián somehow tipped over a shot that was destined for the top corner at close range. Mertens was left in disbelief instead.

Liverpool should have capitalised when Mané beat Insigne to a clearance from a Napoli corner and led a two versus one break deep into the home half. Salah was begging for the ball inside. Mané delayed, delayed and eventually overhit the pass into his unmarked teammate. Unlike at Burnley, it was Mané offering apologies this time.

Salah did get his chance to beat Meret moments later when Manolas miscued an attempted clearance from Koulibaly’s header. The ball dropped invitingly for the Egyptian, who swept a left-footed shot towards the bottom corner only for the Napoli goalkeeper to make a superb finger-tip save.

Liverpool took control against increasingly chaotic hosts as the game entered the closing stages and looked the more likely victor until Mertens invited Callejón to attack Robertson. Everything changed in a VAR moment.