The Reds were blown away by Pep Guardiola's side just after a week after they claimed their first Premier League title in 30 years.
But Klopp says his players were not suffering from a title hangover at the Etihad.
He said: "The game had a lot of key moments and City used them. That is how it is.
"We had our moments where we were really close to make something but City were really there. They used our mistakes, we didn't use their mistakes.
"The game was open but it clicked more for City than for us. But I wanted to see a brilliant attitude and I saw that, the boys were really fighting. Nobody was like 'hey I am coming here, we don't care'. We care a lot. That is how it feels, it feels not good and it should not feel like it is."