The Blues kicked off their Champions League title defence with a 1-0 victory over Zenit St Petersburg.
"We expected a tough game because it's the highest competition in Europe and it's the Russian champions," Tuchel said after the game.
"We had to be at our top level. I am happy because we had to work a lot. It was not easy. It's tough to perform consistently at that level.
"Winning is good for our belief. We are not finished but we are in a good place to improve.
"The first step is done. But there are five more matches to go [in the group stage]."
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