Inter suffered a shock 2-1 reverse against a side residing in the bottom three last weekend, having also been beaten by Sampdoria in the previous game.
Those back-to-back losses have seen them slip behind their city rivals, who have a two-point advantage as both sides chase a top-four finish heading into the final seven games of the season.
"There was a dip that I did not expect," said coach Pioli, whose first game at the helm was a 2-2 Derby della Madonnina in November.
"The important thing is to figure out where we have gone wrong and ensure that does not happen again.
"We have gone over the game against Crotone to prevent it from happening again. We have shown that we are a team and that we have it in us. We let that get away, but we have to produce it again.
"We have to win as many matches as possible. Our duty is to win the derby. We need to read the game well. This is the Milan derby, a vital game for us, for the fans and for the club."