Liverpool play the London side in the Carabao Cup on Wednesday, just three days before meeting again in the league.
Klopp revealed that he believes Chelsea are title contenders, and that he has huge respect for manager Sarri.
"'It is the biggest change I ever saw in such a short space of time," he said.
"Wow. The style is completely different. What a manager he is, to be honest.
"I'm pretty much a supporter of his since I saw him playing at Naples. Outstanding football, and now doing it in a very interrupted pre-season. Eden (Hazard) was not there, (Olivier) Giroud, (N'golo) Kante. Starting the season and you see immediately the impact? All my respect.
"It's really good to watch. Good job so far. People were always talking about Manchester City being clear, and completely forgot Chelsea. This team is really experienced. It won the title before - 80 per cent won it twice, and they know how it works. That's a really strong football team."
Klopp has also revealed that goalkeeper Simon Mignolet will play for the first time since January.