Mariappa hopes the Hornets can use Tuesday's win over Coventry in the Carabao Cup to catapult their poor Premier League campaign.
"I have always believed in the team and the gaffer, and I believe that things will turn," he said.
"Sometimes the luck goes against you in games and in the Premier League there are fine margins.
"But you look at the performances of the last two games and we created a lot of chances and it just hasn't fallen for us. Hopefully today is a good catalyst for us to go on and get a good result on the weekend.
"It is evident to see [what Gracia has done]. We had our highest league position this year with a highest number of points and we made a cup final. I think there is a very good squad here and our levels are always good.
"I think it is a credit to him that now there is a lot more expectation because of how well we have done. Like I said, that's a credit to the gaffer and his management.
"Obviously the boys are buying into the gaffer. For us nothing changes. We are going to a tough place on Saturday but we will be going to try and get some points."
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