Having flopped in this season's Champions League, it would be equitable to pronounce that Manchester City haven't beaten a genuine top-class opponent since April 30th- the ultimately decisive Manchester derby. With the next instalment of the intense Manchester rivalry looming, now would be the perfect time to replicate this feat.

It is much-coveted that the defending Premier League champions, albeit unbeaten thus far, have struggled to rediscover last season's sparkling form in the early months of the campaign, but champions win big games. And no-one needs telling that any game against Manchester United is as big as they come.

Since the seismic Monday night at the tail end of last season in Manchester in which Vincent Kompany's header earned them three points to place them firmly in the driving seat in the title race, Roberto Mancini's men have not been the full package while in some of the big games, they have been missing the key ingredient to come out on top.

The fact of the matter is they remain unbeaten in the Barclays Premier League this term after sixteen games which is an incredible run although in the heavyweight matches against the likes of Chelsea, Liverpool and Arsenal as well as Borussia Dortmund and Real Madrid, they have precariously faltered and haven't issued the statement of intent to convince supporters they are vastly superior above the rest in England and Europe.

Mancini was quick-witted and noticeably during his pre-match press conference. Although inside, Mancini will now there is a notable difference between City's title-winning campaign and this term so far in terms of results, confidence and performances. Last season, City had already beaten Tottenham 5-1 at White Hart Lane and United 6-1 at Old Trafford while this weekend a year ago, they beat Arsenal 1-0 at the Etihad Stadium. Quintessentially, these laid down markers demonstrating their capablities, however, in 2012-13 we have yet to see similar pointers establish with late wins away to West Bromwich Albion and at home to Tottenham being as good as it has got for them so far.

As they finalise preparations ahead of the first meeting with rivals United this season, a derby triumph would be the recommendable tonic to exude confidence and bring the adrenaline rush that their title bid so far hasn't provided. On the campaign, Mancini said to reporters on Friday: "I don't think we have the same quality this season that we showed in the first fifteen games of last season."

"This season we have had big problems with injuries and the year after you win a title is always more difficult. We had a problem with the defence at the start of the season when we were conceding too many goals. Now we have improved that situation but we need to improve the output from our strikers. If we can start to score more, I think we can improve on last season's points total. United have also scored 10 more goals than us. Our season depends on our strikers. If we start to score like last year we will have a big chance."

We are almost at the halfway stage of the season, or exam period if you want to call it that, and if we were to mark City's efforts in defending their title, I would award a grade B. In contrast, I would also award a grade B to United- playing catch-up after last season's heartbreak in losing the title to their "biggest" rivals on the final day- after lacklustre defeats to Everton, Norwich and Tottenham. Yes Ryan Giggs, the biggest.

City cannot escape the fact that even by their own fans' prudent admission, there has only been the odd occasion that the side's potent attacking football has been exhibited this term and playing with the authorative strut which handed them the trophy in 2011-12. Their best form could be compared to the English summer sunshine- it has been in patchy spells. Mancini added: "We've beaten Tottenham this season. We did well in drawing against Chelsea at Stamford Bridge, when all that was missing was a goal, and against Arsenal we deserved to win and they only scored in the last ten minutes to equalise."

"When you consider all the problems we have had since the start of the season, I think it is a good thing that we are only three points behind United." I certainly cannot disagree with this point, hence the separation. However, in comparison to Chelsea's woes on and off the field, City have had it easy.

Despite the doom and gloom surrounding the club this season, City remain very much in the thick of the pack at the summit while when they eventually improve, it could spark a surge in form which could see the club sweep aside opponents in a similar fashion to last term and it could ominously see them over the hills and far away come the end of May.

Across the divide, United manager Sir Alex Ferguson can look at the table with his side sitting top although that could all change in a short space of time. As short as ninety minutes of football on Sunday. Despite being three points clear at the top of the Premier League table, Ferguson's men cannot afford to adopt a defensive approach analogous of the 1-0 reverse last term in which they failed to muster a meaningful shot on target. They certainly cannot rest on their laurels in this game or in the title race.

As Sir Bobby Charlton has pointed out, City do present United with a clear problem when it comes to the physical acumen of the side. Players with the strength and prowess of Yaya Toure and Vincent Kompany will be important in both boxes on the pitch, as will Edin Dzeko if he plays. Mancini admitted last weekend that he opted to withdraw Carlos Tevez as opposed to Dzeko against Everton in order to keep the Bosnian on the field to utilise to his height to nullify the aerial threat of Toffees midfielder Marouane Fellaini.

Ferguson may yet be tempted to throw back fit-again defender Nemanja Vidic into the fray after a knee injury as he looks to add some much-needed steel to the heart of the United back-line. A defence that was distinctly vulnerable in last Saturday's topsy-turvy encounter with Reading which ended 4-3 - a match that illustrated United's issues this term of conceding the first goal (usually early) and relying on their top-quality strikeforce to bail them out and ignite a comeback.

Although they deserve credit for having the character to fight back from a goal down, this is an underlying problem which has gone on for too long in the first four months of the season. It needs addressing as a matter of urgency before Sunday's match otherwise we maybe witnessing an even higher margin of victory for City than a meagre 6-1. Sir Alex will also be hoping for a significant improvement in the goalkeeping facet with mistakes of an incompetent nature shown by both of his first-choice keepers vying for the regular number one jersey in games this week- David De Gea and Anders Lindegaard. Whoever gets the nod on Sunday will have to be on their toes.

Both have Champions League defeats to erase from their systems from a disappointing midweek with City losing in Dortmund and United beaten at home by Cluj. Although it will be City's journey to Germany which may take more out of them and their defeat will hurt more in confirming their exit from European football for this season, which was already on the cards, while United's place in the last 16 of the competition was already booked. Neither side can show visible signs of suffering from a European hangover- not with messrs Ferguson and Mancini in charge, with both bosses making ruthless decisions regarding substitutions and team selections in the past.

Ahead of the latest episode in the derby saga like no other, United appear to have the slightest of edges and a better mindset but that change very quickly as Ferguson will know more than most however it is unclear whether this will place them in the ascendancy when the twenty-two players do battle on the biggest turf in the Premier League. So, forget your roast Sunday lunch for one week and get down to the pub if you have to, this is unmissable.

Follow our Chief Football Editor Adam Higgins on Twitter