The Blues top the standings after seven games following a strong start to the campaign under the German, who is looking to add the league crown to his collection after guiding the team to the Champions League in the summer.
"We want to prove that we deserve to be the favourites and we need a certain mentality to do so," he said.
"If favourite means things will be easy, we can't be more wrong. If being the favourite means we still expect a tough one, then that is what we have to expect. We have to take risks, play with a certain freedom, as with a fear of losing you can win nothing.
"If you work for Chelsea, you play to win. So you can't be surprised if you're the favourites. Does this change our expectation? Hopefully not."
Tuchel warned his players that Brentford will give everything to down the league leaders and challenged them to match their attitude and intensity.
"They will be up for it and play with a lot of enthusiasm and finally Chelsea comes not for a cup game or friendly game," he added. "They have so many points on their side and such good results, they are doing a fantastic job.
"They will play with courage, confidence but we can't be surprised. We know this and it will be on us to adapt and accept the situation.
"They will not gift us a single inch on the field and we have to be ready mentally, physically and tactically. This is not a match about knowing the solutions or trying to out-skill the opponent. We have to match the mentality and attitude."
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