City recorded a famous 6-1 victory in this fixture last season, but the Italian feels that a win of that calibre would be impossible to repeat.
"6-1 is in history," Mancini told BBC Sport. "We can talk about this for another 200 years, but it is impossible to do this another time.
"We know we can beat them [on the day] because they are not better than us. We need to go there thinking we are like them, that we are a strong team like them.
"But they deserve to win this title."
City are in the semi-finals of the FA Cup.