History tells us it is highly unusual for the top two to meet so late in the season with so much riding on the outcome but this has been a highly unusual season.
Sir Alex Ferguson wants that 20th title desperately by keeping City at bay, while others may see Roberto Mancini's team going on to dominate domestically for years to come if they can get that first Premier League under their belt. Has there ever been a bigger Premier League game than this?
In reality City should have had the title sewn up weeks ago in the manner they were playing and the results they were getting. And yet a stumbling run of form away from home gave United a lifeline they were only too grateful to accept to go into an eight-point lead only a couple of weeks ago.
Ferguson's side still have a three-point advantage, so a draw would satisfy them a lot more than City and, unlike their closest rivals, they do not have to go to Newcastle United, a trip not too many would approach with confidence at the moment.
Of course, this being the sort of season it is, you would not bet against further twists and turns even in the final two games. It seems it is destined to go right to the end and United's trip to Sunderland on the last day is no easy job.
Is this because they felt they had nothing more to lose or because they felt the pressure was off as they had finally lost the title race? No-one will know for sure but the pressure is back on them now because suddenly the prize is in sight again.
On recent evidence the key element will be how United's defence copes with City's attack. City have hit that rich vein of scoring form again while United defended abysmally against Everton - although it should be stressed their performances at the back over the recent period have been very good.
And then we come to the Carlos Tevez factor. For so long on the outside looking in at City, with all the acrimony that appeared to accompany that, he is back and doing what he does best.
As long as a player is of use to a football club, and is there at the club, there is always the possibility he will play again - especially if he is of Tevez's quality. And so it has proved, with his performances giving them extra impetus in these crucial final weeks of the season.
When you see him during games he has a great work ethic, sets a great example, and can influence important games. Players will look at him and think that, if he is prepared to put in so much work, they should as well. It sets this good example and makes it much easier to reintegrate someone after a period of disharmony than if they are selfish and not bothered about their team-mates.
Tevez's game is usually raised against his old club anyway, but such is the importance of the match on Monday, he will be vital for City if they are to get the win they need.
I would rather be in United's position than City - but what an opportunity for Mancini's men after their Premier League title race looked to be over a couple of weeks ago.
Alan Hansen was talking to BBC Sport's chief football writer Phil McNulty.
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