Although Mainz lost 3-0 at the Arena AufSchalke, they took all of the plaudits, even from opposition coach Huub Stevens.
However, Tuchel says his side "cannot expect to dominate every game the way we did in Schalke," although repeating the 2-0 win in Wolfsburg would nevertheless be satisfactory.
"We think we can beat them," he added at the pre-match press conference. "It is good that we are all in high spirits and we certainly have the will to win."
Should Mainz succeed, they would become the first team in the Bundesliga this season to defeat the top-flight newcomers.
Fortuna's defence leaked its first goals of the campaign last weekend in a 2-2 draw with Schalke, but Norbert Meier's troops have so far managed to pick up at least a point in all of their matches since re-joining the big boys after a 15-year absence.
However, they are not getting carried away with their start to the season, according to Oliver Fink.
"We have played quite well and got 10 points and nobody had expected that," he said in the Express newspaper.
"But it is nothing more that than. With 10 points (at the end of the season), you are relegated."
Team mate Axel Bellinghausen echoed Fink's words, saying: "We are not so short-sighted to run around and think things will just carry on like this. No, we know it is going to take a lot of hard work."
Meier may rotate his attack again tomorrow [Saturday] with Ken Ilso in line for a return for Andriy Voronin.
Tuchel could have Junior Diaz available after injury while Zdenek Pospech and Nicolai Muller are also options.