The victory for the Blues -- Tuchel's first over Guardiola -- contrasted with a 3-1 drubbing at home by City in early January, which hastened the departure of former Chelsea boss Frank Lampard and his replacement by Tuchel.
"If you play against Pep, you know that you play against the highest level in Europe because everywhere where he was on the sidelines, with Barcelona, Bayern Munich and now Manchester City, he was the benchmark for years with his teams and he is again," Tuchel said.
"Our target is to close the gap for the 90 minutes because it's possible in football and if you arrive in a good momentum, you can make this happen," he said.
"I am very, very happy and proud of the performance of our team because we played with a lot of courage."
Saturday's win -- secured with a 55th-minute goal by Morocco forward Hakim Ziyech -- leaves Chelsea in the hunt for silverware in the May 15 FA Cup final against either Leicester City or Southampton, and in the Champions League with a semi-final clash looming against Real Madrid.
Tuchel said beating Manchester City would give the young players in his squad a confidence boost but he reminded them that they now faced a "crucial week" in the Premier League.
Chelsea host Brighton on Tuesday and travel next Saturday to West Ham United who are locked in a battle with the Blues for a top-four finish.
Guardiola congratulated Chelsea for their win but said the match could have gone either way.
"It was a tight game. Anything could happen," he said.
The Spaniard bristled when asked by a reporter whether his decision to make eight changes from the side which beat Borussia Dortmund in the Champions League midweek had contributed to the defeat.
"I am delighted with what we have done so far. The amount of games we have played... and all the players make absolutely everything," he said. "Do you think we don't pay attention in the game?"