Holders Liverpool and Frank Lampard’s Chelsea still learning lessons in Champions League

On a balmy night at the intimidating Stadio San Paolo, the Reds fell behind in the 82nd minute when Mertens converted from the spot after Andy Robertson had upended Jose Callejon in the area.

Substitute Llorente – part of the Tottenham side beaten by the Reds in last season’s Champions League final – then took advantage of a mistake from Virgil Van Dijk to bag his first goal for Napoli after joining them earlier this month.

Liverpool have started their Premier League campaign with five successive victories but largely struggled for composure in their Group E opener, while they lacked a clinical edge on a night where they were barracked throughout by a boisterous home support.

They were indebted to a couple of crucial saves from goalkeeper Adrian for keeping the scores level and, though Roberto Firmino and Mohamed Salah went close for the visitors, their errors in the latter stages proved costly.

This was their second defeat in Naples inside a year, having gone all the way in Euorpe’s elite club competition despite losing all three matches away from Anfield in the group stage last season.

Liverpool captain Jordan Henderson rued his side’s lack of cutting edge.

“(In the) first half I still felt we played some good stuff, it’s that final bit we were just missing today. At home Napoli are a good side, they are going to create some chances,” he said.

“You’ve got to be prepared to defend as a team which again, I felt we did. We won some great balls in midfield and counter-attack, but it was just that last little bit and then obviously the mistakes. Overall, we can be better of course, and like I say we’ll take responsibility. We’ll move forward and try and react in the right way.”

Ross Barkley fluffed a late penalty as Frank Lampard suffered defeat on his Champions League debut as Chelsea manager.

The Blues, trailing to a goal from Valencia winger Rodrigo, were given a lifeline in the closing stages when VAR flagged up a handball in the area.

Barkley was involved in a debate with team-mates Willian and Tammy Abraham over who should take the penalty.

The former Everton man won the argument, but then saw his spot-kick clip the crossbar to condemn Lampard and his young side to a 1-0 loss in the Group H opener.

The Spaniards were supposed to be there for the taking, having arrived in west London in turmoil following the sacking of popular boss Marcelino last week. But they did not play like a team on the verge of mutiny and had too much nous for Lampard’s beginners, four of whom were making their Champions League debuts.

Lampard said: “We shouldn’t lose the game. Clearly. At least not lose it. We had a fair few chances. And then the penalty, which we miss. We have to keep our heads up. There is a long way to go. It is a lesson.”

But the former Blues player – and penalty taker – refused to blame Barkley after his costly miss.

“Ross is a penalty taker and is when he starts games. He took it and missed it. It is a great story to say there is contention between players. If he scores it is not a story,” he said.

“But he took it and missed. That is it. The disappointment to all of us is that we didn’t get chance to win the game. There is no issue in the dressing room.”

He added: “I saw Liverpool lost tonight. This is the Champions League and there are tough games. There will be bumps in the road for us with the youth and changes we are trying to make. But we need to be strong with Liverpool here at the weekend.”

Lampard, who played 102 Champions League matches for Chelsea and captained them to their 2012 triumph, was perfectly placed to impart his experience of playing at this level to his youngsters - but it could still be a steep learning curve this season.

Tammy Abraham, fresh from his hat-trick at Wolves, was denied a maiden Champions League goal when his near-post flick was blocked by Valencia keeper Jasper Cillessen.

Fellow rookie Mason Mount then received a painful introduction to Europe when former Arsenal midfielder Frances Coquelin left his studs on the inside of the youngster’s shin.

It was a nasty challenge which only earned Coquelin a yellow card, but after trying to play on Mount’s match came to a premature end after 14 minutes.

Abraham went close again with a far-post header from Cesar Azpilicueta’s cross and Willian’s powerful run through the middle only produced a shot which flew wide.

Willian, Chelsea’s biggest threat in the first half, almost fashioned a spectacular opener when he controlled Mateo Kovacic’s crossfield pass on his chest, but his first-time shot flew over.

And on the stroke of half-time the Brazilian’s fierce drive towards the near post was parried clear by Cillessen.

Marcos Alonso took the game to Valencia early in the second half, drilling in a free-kick which Cillessen tipped behind before heading the resulting corner over.

But in the 74th minute they fell behind, Rodrigo giving the Chelsea defence the slip as he raced onto Daniel Parejo’s chipped free-kick and swept the ball past Kepa Arrizabalaga.

The drama reached fever pitc