Liverpool manager Jurgen Klopp was left fuming after VAR missed what he deemed a "clear and obvious" dive that led to a controversial penalty in the 2-0 defeat to Napoli on Tuesday.
The champions of Europe got their title defence off to the worst possible start, going down 2-0 in Naples. Dries Mertens slotted home an 82nd-minute penalty fter Jose Callejon went down easily under pressure from Andy Robertson, before a misplaced pass from Virgil van Dyjk allowed Fernando Llorente to capitalise in injury time.
Felix Brych’s decision to award a penalty against Robertson was not deemed a clear and obvious error by VAR, however, leaving Klopp to lament the regulations.
"I don't think it's a penalty," Klopp told BT Sport. "What can I say, for me, it is clear and obvious, no penalty. He jumps before any contact, we can't change that.
"We played a lot of good football but didn't finish it off."
The defeat means Liverpool became the first European Cup holders to begin their title defence with a defeat since AC Milan in 1994.
The usually prolific front three of Mohamed Salah, Sadio Mane and Roberto Firmino were all guilty of wasting chances.
"It should hurt because there were opportunities for us," added Klopp. "It was an open game with a lot of counter-attacks, but we didn't finish them off and that is a problem.
"We controlled moments but had not enough chances in the end. We made decisions that were not right and have to accept the result.
"It was very often the final ball that was not right."
Hirving Lozano thought he had made the early break through when he headed in from close range but the Mexican's effort was correctly ruled out for offside.
Mane, whose four goals in five games have propelled Liverpool to the top of the Premier League, forced Napoli goalkeeper Alex Meret into a smart save and Firmino flashed a header from the resulting corner wide before the break.
An Alisson save in the corresponding fixture at Anfield last season, when these two sides also met in the group stage, was widely credited with keeping Liverpool in the competition and allowing them to go on to life a sixth European Cup in June, and the Brazilian's Adrian emulated his teammate with a spectacular stop of his own early in the second half to deny Mertens' close-range volley.
Meret pushed a Salah effort wide with Liverpool's grip on the game tightening before the "game-changer", as Klopp put it, turned the match as Callejon burst through into the area and Liverpool left-back Robertson was adjudged to have fouled the Napoli man.
As Liverpool pushed forward for an equaliser, Van Dijk played a hasty back-pass straight to Llorente and the former Tottenham Hotspur striker, who played against Liverpool in last season's final, sealed the English club’s fate by prodding home his first Napoli goal.
“We worked hard to defend and attack as a unit, because at times football means adapting to situations and I think we did it well,” Napoli manager Carlo Ancelotti told Sky Sport Italia.
“We felt confident on the second goal, it was near the end and we were a goal up. You can press high at times, not at others, it’s about maintaining your identity and also being able to do everything. I liked our quality, but also how we played ugly when we needed to.”
Liverpool must now bounce back in two weeks when they host Austrian champions Salzburg, who made a stunning return to the group stage as teenage forward Erling Braut Haaland netted a hat-trick in a 6-2 demolition of Genk.
Haaland, the teenage English-born Norwegian striker whose father Alf-Inge played for Leeds United and Manchester City, gave Salzburg a second-minute lead and netted twice more before half time.
Aged just 19 years and 58 days, Haaland is the third-youngest player to score a Champions League hat-trick behind Wayne Rooney and Raul.