Mata is becoming increasingly influential under manager Roberto di Matteo.
Asked how the Blues could continue to perform after scoring a 93rd-minute winner in what was the first of another six games in 18 days, he said: "With faith, with faith.
"We are in a crucial moment for us. Next week, we are playing in the FA Cup semi-final, Champions League, still fighting for the third and fourth position in the Premier (League).
"The faith, I think, is more important than the muscles or feeling tired.
"So, we are training well to be ready for Monday."