It has been a tough period for Manchester City with the club crashing out of Europe, but a strong performance against rivals United on Sunday in the derby would turn their season around.
There is an incredible imbalance in the United side, and if City play anywhere near their best as a collective unit with their key players firing, they will come out on top.
It is often said, rightly, that big games such as this are decided in the midfield, and that will certainly be the case on Sunday. There is no doubt in my mind that City have a hugely dominant midfield, and that will be the difference between the sides once more.
United have often given teams head starts this season, and their over-reliance on their firepower in attack is really quite staggering. They cannot afford to give City an early lead, because there is only so long the forward can continue to bail the team out.
Sir Alex Ferguson's midfield are often wasteful on the ball, and less than dynamic off it, which has to be regarded as a major problem against a side with as much quality as City possess.
There is no way that Darren Fletcher is back to his best; Tom Cleverley is due to have a calf scan and I do not believe he is worthy of much of the hype which continues to surround him; Paul Scholes is increasingly limited in what he can offer around the pitch; and Anderson is, well, Anderson - he just doesn't do enough.
One key battle for me will be if Mancini decides, as he should do, to give Yaya Toure back his free role and push him on to disrupt the time and space that Michael Carrick and Scholes have at the base of the United midfield. If he can play havoc with the pair, City will win fairly comfortably.
I do not think City need to play five men across the midfield, and can get away with having Gareth Barry in his usual holding role and letting David Silva and Toure do what they do best, buzzing around him, with Carlos Tevez and Sergio Aguero up front.
Jonny Evans has a tendency to abandon his positional discipline and to fall half-asleep at crucial moments in matches, and the United defence barely receives any assistance from the midfield, which leaves them open and vulnerable.
What is absolutely vital for City is that Mancini settles on what is his best line-up and formation, because he seems to have forgotten what won him the title last season with some of his needless tinkering and unnecessary changes.
We simply have no idea what Mancini is capable of, or what he regards to be his best XI, which has to be a real concern for the supporters, while it is unsettling for the players.
Joleon Lescott was an ideal partner for Vincent Kompany last season, and the City captain has not looked the same since the Englishman has been confined to the bench this campaign; the Italian is missing the point if he is looking at their displays as individuals, because it was their partnership and understanding that made them both look good.
Equally, Toure has had to rein in his attacking instincts in a more reserved midfield role. For a key player that made the difference time and again last season, it really is inexcusable how much he is being asked to sit in and contain. On his day, he is unplayable, and there is no one else in the Premier League who can do what he does.
Mancini is the weak link for City, and if I were a supporter of the club I would be very concerned with the prospect of him attempting to be overly clever in his approach to this match, when it was doing the basics effectively that was responsible for beating United at the tail-end of last season.
It's very difficult to know whether it is a positive thing for City's title campaign that they are no longer in Europe, because on the one hand they have fewer games, but Mancini also has to juggle his huge squad around while keeping everyone happy.
City have to attack United and attempt to exploit their weaknesses; they have to be aggressive and positive and look to take all three points from the game, not just a draw.
United will be happy to take a point from the match, but Mancini has to look to win the game and to respond to his side slipping out of Europe with an encouraging performance to give confidence back to the team and to the supporters.
This is the biggest game of the season for Mancini, and he simply has to do away with his constant tinkering and focus on giving his side the best possible chance of playing to their strengths and winning the game.