An exultant chorus of Allez, Allez, Allez filled the Stadio San Paolo after the final whistle but not the version that accompanied Liverpool all the way to last season’s Champions League final. It reverberated with a Neapolitan voice. Only they had cause to celebrate. Only their team delivered. Liverpool were silenced.

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A slender Napoli win courtesy of a 90th-minute winner may indicate misfortune for Jürgen Klopp’s team. The story of the contest was much different. Liverpool, not to put too fine a point on it, were unrecognisable. Uncharacteristically subdued, error‑strewn and on the back foot throughout, the visitors did not produce one shot on target against Carlo Ancelotti’s side and Lorenzo Insigne’s late winner was the least Napoli deserved. The momentum produced by that dramatic stoppage-time win against Paris Saint-Germain has been squandered by last season’s finalists.

Klopp identified the failing that led to Insigne’s decisive tap-in from José Callejón’s low cross – “We didn’t close the gap between Joe [Gomez] and Virgil [van Dijk]; another tactical mistake” – but struggled to explain his team’s worst display of the season overall. It was as weak as it was unexpected and the Liverpool manager said he will need to review it before reaching conclusions. It will be painful viewing.

Quick guide Champions League results Show Hide Tuesday 2 October Group E: AEK Athens 2-3 Benfica, Bayern Munich 1-1 Ajax

Group F: Hoffenheim 1-2 Man City, Lyon 2-2 Shakhtar

Group G: CSKA Moscow 1-0 Real Madrid, Roma 5-0 Plzen

Group H: Juventus 3-0 Young Boys, Man Utd 0-0 Valencia Wednesday 3 October Group A: Atlético Madrid 3-1 Club Brugge; Dortmund 3-0 Monaco

Group B: PSV 1-2 Internazionale; Tottenham 2-4 Barcelona

Group C: PSG 6-1 Red Star Belgrade; Napoli 1-0 Liverpool

Group D: Lokomotiv Moscow 0-1 Schalke; Porto 1-0 Galatasaray

Latest Champions League table Photograph: Kieran McManus/Rex Features

He had described Ancelotti as a “smart fox” and the three-times Champions League-winning coach lived up to the pre-match description. The Italian deployed a third centre‑back in his starting lineup, Nikola Maksimovic, to prevent a repeat of the 5-0 friendly defeat by Liverpool in Dublin in August; an experience that Klopp insisted would have no influence on a competitive European tie.

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Ancelotti said: “We played with an extra central defender because Sadio Mané and Mohamed Salah targeted our two centre-backs in the friendly. That’s what they do and it creates space for Roberto Firmino. We wanted to stop that and we did.”

Napoli were the more threatening team throughout, too.

The San Paolo may be crumbling in places but remains an atmospheric arena that can test seasoned Champions League travellers. Locals were queuing for the beat seats in the old house more than three hours before kick-off as Napoli endeavoured to capitalise on home advantage following a disappointing goalless draw at Red Star Belgrade. Not that it was full, however, and Liverpool’s difficulties were of their own making rather than any external noise.

Naby Keïta replaced Jordan Henderson in the only change to the Liverpool team who drew at Chelsea on Saturday and set the tone with a series of misplaced passes during his 19 minutes on the pitch. Two mistakes almost led to clear chances for Insigne, who was denied one by Van Dijk’s interception and shot narrowly wide of Alisson’s far post after the £52.75m midfielder had sent a loose ball to Callejón.

Facebook Twitter Pinterest Napoli’s Lorenzo Insigne slides in to score the winning goal. Photograph: Ciro de Luca/Reuters

Keïta’s night was over minutes later when he injured his back in a collision with the matchwinner Insigne. The midfielder’s distress was obvious as he received lengthy treatment before going off. A worrying sight for Klopp, regardless of the Guinea captain’s difficult night on the ball, and cue for Henderson’s swift return.

Liverpool’s problems were not confined to wayward passes in the heart of their midfield. Napoli regularly broke behind the outnumbered Trent Alexander-Arnold at right-back. To the annoyance of the home crowd they were unable to capitalise because of a recurring fault – a dreadful final ball. When Arkadiusz Milik opted to find Insigne inside the penalty area rather than shoot, and overhit his pass straight out of play, the San Paolo howled in disapproval.

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Patience had been stretched by several similar errors although Milik was closest to opening the scoring in the first half when he turned Van Dijk on the penalty spot and tested Alisson with a rising shot.

Milik forced Alisson into another sharp save early in the second half as Napoli restarted with an intensity and purpose that Liverpool lacked. The Poland international took aim from almost 30 yards with a low drive that Alisson blocked at full stretch to his left. Gomez was crucially on hand to clear before Insigne could snap up the rebound. From the subsequent corner Fabián Ruiz shot straight at Liverpool’s overworked keeper. The pressure was growing, as were the number of unforced errors from Liverpool.

Van Dijk denied Insigne with a perfectly timed tackle at the near post after Milik released Mário Rui for an inviting cross from the left.

Seconds later the Netherlands defender gifted possession to Milik inside the Liverpool area and was reprieved when the striker over‑elaborated yet again – prompting further derision from the Napoli crowd – and allowed Alexander‑Arnold to intercept.

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Alisson was not immune to errors in possession either, gifting the hosts the ball with one misplaced chip. Gomez helped retain parity with a goal-line clearance from Callejón but Dries Mertens, the Napoli substitute, should have opened the scoring when found unmarked inside the area by Rui’s delightful cross. Mertens volleyed against the bar instead and Liverpool appeared reprieved.

It was a misconception. In the final minute Napoli broke down the right with Van Dijk dragged over to the touchline and Andy Robertson unable to catch Callejón’s run into the area. The cross eluded Liverpool’s retreating defence, Gomez lost Insigne and the striker slid in to convert. There could be no complaints.