Liverpool endured a stunning return to action as City, the side whose Premier League crown they took last week, served a ruthless reminder of their quality at the Etihad Stadium on Thursday.
Kevin De Bruyne began the rout from the penalty spot before further goals from Raheem Sterling and Phil Foden before half-time. An own goal from Alex Oxlade-Chamberlain completed the rout.
After finally ending a 30-year title drought and losing just one other match all season, Liverpool could perhaps be excused an off-night. But manager Klopp insisted his side were still on top of their game.
"It has nothing to do with last week. It hurts like defeats hurt," he said.
"What I wanted to see was who is ready to fight against Man City, who obviously had a point to prove. It was easy motivation for Pep.
"We were in the game, we were fighting, we were running. We did everything we could. Was it perfect? No. The problem is if you are not perfect and meet Man City, then you lose, and the result can be not so nice.
"If there is a team in the world that can smash us like this it is probably City, but we will come again."
Meanwhile, Raheem Sterling said Manchester City proved a point to the newly-crowned champions.
"We had a test against the current champions to make a point and we did brilliant," said Sterling. "Next season started today and we did well."
City manager Guardiola is hoping the manner of the victory can spur his side on to finish the season on a high by succeeding Liverpool as Champions League winners.
"It is important," said Guardiola. "Especially because they were incredibly focused."
"I'm delighted. Congratulations to the team, we beat the champions with the quality they have.
"I saw in the guard of honour how incredibly focused they were, how they shouted. I saw their faces, that's why they're champions.
"So the chances we created, to beat them 4-0, it was so important for preparing against Arsenal and Real Madrid."