"It is important to win so we don't lose more ground on Juventus. Before trying to reach them it is obviously important to overtake who is in front of us," Mancini told Inter's official website on Saturday.
Inter have 29 points in the fourth place, two points and one spot behind last season runners-up Milan with Juventus leading the standings on 39 points.
But Mancini said that Sunday losers won't be out of the title race because "There are still too many matches to play. Also, I think that sooner or later Juventus will slow up."
Asked about how he would face Inter's former striker Christian Vieri, he said the Italy international is just as dangerous as any Milan player.
"Vieri is one of Milan's many champions. If he plays we will have to be careful of him just like all the others," he added.