Lukaku gave a controversial interview to Sky Sports Italia last week in which he revealed his frustrations with the Chelsea boss, with it costing him a place in the Chelsea squad for the home draw to Liverpool.
However, he has since apologised and smoothed things over with Tuchel, and he returned to the side in the semi-final win over their London rivals.
"I'm happy with his performance, I like how he played, strong, huge commitment in defensive work," Tuchel said after his side's 2-0 win.
"He was always dangerous, always used his body, and was always involved in dangerous situations. I expected it honestly because Romelu can handle pressure, he can handle adversity, and he seemed to be relaxed after the decision was made and we finished our talks. I felt him relaxed enough to have a performance like this."
"Kai has the issue with his finger, he broke his finger and it looked horrible," said Tuchel.
"And he played through the pain that was getting bigger and bigger. He survived until half-time and then we had to make the change.
"I liked our performance a lot. We looked full of confidence and had two late last-minute pieces of bad news with Thiago Silva and N'Golo Kante, who were both supposed to start.
"So we decided at the last minute to maybe switch to a back four. The guys were very committed and very open to that, to making such a late change.
"And it was a very strong performance, so it was a well-deserved win in a big match against a very strong opponent."