The injured Brazilian was seen in the stands reacting to Emerson's late goal in victory over Atletico Madrid that confirmed Chelsea's progression to the Champions League quarter-finals, where they have been drawn against Porto.
And Tuchel said the celebrations, alongside Mason Mount and Jorginho, were typical of the veteran central defender.
He said: "I know Thiago for many years now. We had a fantastic partnership in Paris, a completely reliable captain for me from the minute I stepped in.
"Once he is part of a team, he is 100% part of the team, 100% professional. He is a very emotional guy.
"All three of them, Mason, Jorgi and Thiago, were completely involved in the game and that makes them involved in the moment. I heard them during the game coaching and supporting the players. I had the same thing from Willy and Kepa on the bench."
He continued: "To create an atmosphere like this, you can rely on Thiago. He was so, so happy for Emerson to score like the other guys.
"He rans the stairs up and down and was dressed like a 28-year-old!
"On his contract, it is too early. Me and the club will make this decision together but if you look at the pictures, you can see how young he looks."
Tuchel's side face Porto in what on paper looks like the soft route to the semi-final stage of the Champions League.
But the German warned that it will not be an easy game. He said: "Clearly, many people will now make us favourites against Porto but that will not help us. You can ask in Turin if that helps you.
"We are self-confident and that is strongly connected with our performances. So we are confident that we will face a strong opponent and face them with respect, but we are in the quarter-final and are focused on winning that."