Jurgen Klopp questioned the awarding of a penalty to Napoli which he felt proved decisive as Liverpool started the defence of their Champions League crown on a bum note.
The Reds lacked a cutting edge but would have been worthy of a point at the intimidating Stadio San Paolo, only for the Group E opener to hinge on Jose Callejon being upended in the area by Andy Robertson.
Dries Mertens converted from the spot in the 82nd minute before Virgil Van Dijk lost the ball on the edge of the area in stoppage time, allowing former Tottenham striker Fernando Llorente to seal a 2-0 win for Napoli.
Liverpool manager Klopp said:
The Reds' strong appeals for a penalty against Newcastle at the weekend fell on deaf ears but they maintained their 100 per cent winning start to the Premier League season by beating the Magpies 3-1.
Tuesday night's decision proved central to the outcome but Klopp refused to be too critical of the process involving the video assistant referee.
The visitors, barracked throughout in a hostile atmosphere in Naples, lost the corresponding fixture between the sides last season en route to being defeated in every group stage game away from Anfield.
The Merseysiders managed to pip Napoli to the knockout stages by virtue of goals scored and went on to lift the European Cup for the sixth time in their history.
Klopp believes Napoli are more than capable of going all the way this season.
Napoli counterpart Carlo Ancelotti welcomed Klopp's assessment of his side as potential winners.
The Italian said:
Ancelotti shied away from talking about the penalty award, preferring to focus on his side's display.