Liverpool's UCL defence begins with Napoli loss

Liverpool opened their Champions League title defence with a 2-0 loss at Napoli on Tuesday as Reds manager Jurgen Klopp questioned the decision to award a late penalty to the Serie A side.

Dries Mertens converted a penalty eight minutes from the end of an entertaining match after a contentious foul by Andy Robertson on Jose Callejon. Substitute Fernando Llorente then sealed it in stoppage time with his first goal for Napoli -- a measure of revenge after playing on the Tottenham side that lost last season's final to Liverpool.

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Liverpool became the first reigning champions to lose their opening game since AC Milan were beat by Ajax in 1994. Liverpool coach Jurgen Klopp thought that Callejon accentuated the foul after Robertson was adjudged to have tripped the Spaniard in the area.

"I'm pretty sure there are different views on that. When a player jumps before there is contact it is not a penalty," Klopp said.

On the first night of VAR use in the group phase, Klopp wondered aloud how the referees came to the decision.

"I'm not the best loser but I'm not a bad loser. It was a decision made by human beings. As long as human beings make the decisions there is potential for failure. The referees and the VAR were all German, and they have experience with the VAR in Germany," said Klopp, who is also German.

"I'm sure they will find an explanation on why they did the right thing."

Still, Klopp was not altogether discouraged.

"That was the game changer tonight and we have to accept the result," he said. "We are really critical with ourselves but it was not a really, really bad performance."

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Last season, Napoli also beat Liverpool 1-0 at home before the English side won by the same score in England -- denying Napoli a place in the knockout rounds. Napoli and Salzburg, which routed Genk 6-2, took the early lead in Group E.

"I hope it's not decisive," Klopp said. "Give us at least a few more games to change the table."

The atmosphere inside the newly renovated Stadio San Paolo was electric from the start as both sides attacked relentlessly from the opening whistle. Napoli countered Liverpool's established attacking trio of Mohamed Salah, Roberto Firmino and Sadio Mane with a lineup featuring four forwards: Lorenzo Insigne and Callejon on the wings surrounding Mertens and Hirving Lozano.

"It was very balanced match," Napoli coach Carlo Ancelotti said. "They're the best squad in Europe and they were again tonight, because they forced us to be extraordinary."

Salah was on full sprint from kickoff but couldn't find a way past Napoli's center back Kalidou Koulibaly. Liverpool goalkeeper Adrian -- in his Champions League debut -- denied Fabian Ruiz twice in one action before Lozano headed the second rebound into the net only to be whistled offside.

As dazzling as the offensive display was, the defense was just as impressive. Joel Matip lunged to head away a cross intended for Lozano that seemed a sure goal then Ruiz sprinted back at the other end to intercept what would have been a tap-in for Salah.

The frantic pace continued, with Firmino heading just wide of the far post from a corner in the 44th. Possession in the first half was split exactly 50-50. The fireworks continued immediately after the break when Adrian hung in the air to deny a volley from Mertens with one hand at the far post.

There was a rare defensive mistake when Kostas Manolas gifted the ball to Salah in a great position but Napoli goalkeeper Alex Meret extended to glove the Egypt international's shot wide.

It was only in the last 15 minutes that the pace slowed, with both teams visibly exhausted on a warm evening. Then Napoli found the breakthrough with the penalty. Adrian lunged to his left and got a hand on Mertens' spot kick but couldn't stop it.

In the final minutes, Napoli fans' whistled so loud every time Liverpool had possession it was deafening, and it seemed to have an effect when Virgil van Dijk gifted the ball to Llorente, who rolled it past Adrian with ease.

"We put in practically the perfect performance," Callejon said. "We've faced them so many times that we know them tactically by now and did everything right."

Meanwhile, Ancelotti -- who added another chapter in his long, personal history against Liverpool -- consoled Klopp.

"I told him to relax, because if he loses here, he tends to go on and win the Champions League," Ancelotti said. "I reassured him."

In the other Group E game, Salzburg made an impressive start with a 6-2 victory at home to Genk.

Erling Haland scored a first-half hat-trick for the Austrian champions, becoming the third youngest player to net a Champions League treble at the age of 19 years and 58 days, behind Raul (18 years and 113 days) and Wayne Rooney (18 years and 340 days).