A Gabriel Jesus strike early in the second half was enough to give Manchester City all three points at Stamford Bridge.
From minute one, Chelsea struggled to get a hold of the game as City were so dominant on the ball throughout the first half.
In the second half, City's efforts were rewarded with a goal. Despite Chelsea's best efforts, Tuchel's side failed to draw back level.
Here are the five things we learned from Chelsea's defeat:
1) The Blues severely struggled with City's press
With Mason Mount out with an injury, Thomas Tuchel opted to pack the midfield. The likes of Jorginho, N'Golo Kante and Mateo Kovacic started against Manchester City. From minute one, Chelsea's backline struggled deeply with City's press. With the Blues opting to play out from the back, City's forward line were quick to get up the pitch and pile the pressure on Chelsea. Throughout the entirety of the game, the likes of Gabriel Jesus, Jack Grealish and Bernardo Silva made life hard for Chelsea's defence in what was a poor display from Tuchel's men.
2) Chelsea lost the vital battle in midfield
In the showdown with Manchester City, Tuchel decided to start three out and out midfielders to try and match the midfield of City which included De Buryne, Rodri and Bernardo Silva. With Chelsea struggling with the press, the Blues' midfield had to get the ball up the pitch. With that being said, the midfield of Chelsea struggled immensely. Kante, Jorginho and Kovacic all lost the first and the second balls which allowed City to control the centre of the pitch.
3) Without Mendy, it could've been a lot worse
Since joining Chelsea last season, Edouard Mendy has proved that he is one of the best goalkeepers in the league. His sheer presence at the back is a breath of fresh air for the Blues. Throughout the majority of the game, City were ruthless in the final third. With that being said, Mendy stepped up for Chelsea when the side so desperately needed it.
4) Timo Werner and Romelu Lukaku were mere passengers
In the Thomas Tuchel era, Chelsea have had a lot of joy against Pep's Manchester City. The way the Blues played in behind City's backline helped Chelsea gain all three points against Pep's men in the past. Therefore, Tuchel decided to start Timo Werner to try and get the Blues forward in the final third. Unfortunately, both Werner and Lukaku had a little impact throughout the game due to the fact that the pair never received the ball. At times, when they did get a hold of the ball, they made a slight impact.
5) The most negative performance under Tuchel to date
Going into the game with City, the Blues were top of the league. Chelsea had the chance to make a statement against the champions of England. With that being said, it was all but that. Right from the get-go, the Chelsea side were negative in their approach and got battered in midfield. By the time Tuchel changed the system, it was too late. Pep's men had the lead and were able to see out the game. Despite the defeat, it's only one game. There's still plenty of time to turn it around.