Sergio Aguero missed a penalty as the Blues snatched a 2-1 Premier League win at the death to delay City's title-winning party.
Victory over the side they will face in the Champions League final in three weeks' time would have seen City confirmed as Premier League champions for the third time in four years on Saturday.
Despite taking a first-half lead through Raheem Sterling, record goalscorer Aguero then embarrassingly fluffed his lines from the spot and Hakim Ziyech levelled for the Londoners after the break.
Marcos Alonso then grabbed the winner deep into injury time from a Timo Werner cross.
And speaking to talkSPORT, Tuchel lavished praise on his men as their brilliant run of form continued.
"I felt we were very brave," he said.
"I had the feeling we were constantly on the edge to score a second. I don't want to hide it but you need luck when you play Manchester City.
"With the penalty that Edou [Mendy] saved and the second penalty we didn't concede.
"It was a soft decision. It was a 40-60 but maybe that was the reason why the second 50-50 was not given."
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Tuchel admitted the match could have been very different had Aguero converted from the spot.
"If they score the penalty maybe it is over before it starts, at 2-0 you have no chance to come back," the Chelsea boss said on Sky Sports.
"I was impressed by the reaction and the performance in the second half.
"If you want to steal all three points here after being down, you need a bit of luck, decisions from the referee.
"It was a bit like this, but we had some chances in the second half and a big congratulations to the team."