Jurgen Klopp said Napoli can win the Champions League, while the Liverpool manager backed his team to bounce back from their defeat.

Defending champions Liverpool were beaten 2-0 by hosts Napoli in a controversial Group E opener on Tuesday.

Dries Mertens converted an 82nd-minute penalty after Jose Callejon appeared to go down under minimal contact from Andy Robertson at Stadio San Paolo, where the referee's decision was ratified by a VAR check, and Fernando Llorente sealed the win.

Liverpool manager Klopp, whose side lost 1-0 to Napoli in last season's group stage, was frustrated with the penalty decision afterwards and when asked about the Champions League chances of Carlo Ancelotti's side, he said: "They can win the competition, that’s how it is.

"If you have a good plan, if you have good players, which is what they obviously have, then they can win the competition. We experienced that you don't have to be the best team in the world to win the Champions League.

"You have to be in the right moment, you need to be lucky in some situations and when there's only two guys in the room that think it's a penalty you still have to accept that's a penalty, but that's all. They can win the competition, of course."

Klopp was pressed as to whether Napoli were fresher and finished stronger than Liverpool due to Serie A starting later than the Premier League, and the German was not happy.

"Tonight, the questions are really a challenge, to be honest," Klopp said. "I think the guy from Sky Italia asked me or told me Napoli was much better than us. I didn't see that game, so I don't know exactly where he was when the game happened.

"But now you say we were tired. Who had the cramps? Who was on the ground? Liverpool players or Napoli players? After the 2-0 they looked fresher than us, after the 1-0 they looked fresher than us – that's normal. You have a boost. But there was no fresher team on the pitch. There was no physical problem apart from the normal physical problems in a game like this, which is very intense [because] both teams fight hard and all that stuff. It's not a physical problem tonight.

"We have to finish the situations off. How everybody is in life, you need positive moments and you can run forever. We didn't have really positive moments tonight. They obviously got the second air, so they could go again. That's normal, but that was not the reason."

Klopp added: "I hope it [the result] is not decisive. Give us at least a few more games to change the table. In the moment it looks like Napoli’s through, but we still will be playing. We will not stop."