Sunday's meeting of the Manchester teams will capture the attention more than the imagination. United's worldwide following will be glued to their television screens while support for City will range some way beyond the Knutsford service area. Yet the result is likely to command more interest than the performances since neither side is playing consistently well.

In fact the thought of the Premier League developing into a Manchester duopoly over the coming seasons is depressing not only because of what may or may not be happening at Old Trafford and the Etihad but because the strength of other likely challengers appears to be on the wane. The championship can do without becoming one long derby involving an infirm Old Firm.

Since the Premier League plutocracy broke away from the Football League 20 years ago Manchester United have won the title a dozen times and Manchester City once; last season, when goals from Edin Dzeko and Sergio Agüero overturned Queens Park Rangers' 2-1 lead in stoppage time to snatch the title from United, who thought they had done enough by winning at Sunderland. This was something refreshingly different but such a denouement is unlikely to be repeated.

The fact that United ran their neighbours so close could not have been foreseen the previous October when City won 6-1 at Old Trafford to take a five-point lead over Alex Ferguson's team at the top of the Premier League and go 12 ahead on goal difference. At that stage Roberto Mancini's side were setting awesome standards in both attack and defence that suggested a fundamental power shift was taking place in Manchester football.

After 15 games last season City led the table by two points from United having won 12 games, drawn two and lost one with 49 goals scored and 15 conceded. Now they are unbeaten after 15 matches but crucially have won only nine times, with six draws, while scoring just 28 goals. A win on Sunday would continue the Mancunian leapfrog and take City back to the top on goal difference but already the act is looking a little weary.

Not that United appear to be in much better shape. While their league record is much the same as it was at this stage last season, when 15 matches had also brought them 36 points, the number of times they are having to come from behind to get a result is surely a sign that the old omnipotence is getting a bit rusty.

The rapid exchange of goals at Reading last weekend from which they emerged with a 4-3 win could not hide the fact that their defence is now repeating on a regular basis the shortcomings so ruthlessly exploited by City at Old Trafford last season, when United went down to 10 men. Frequent injuries among the back four have not helped and at least the will to win among United's players is as strong as ever. Thoughts of losing never enter their calculations.

What goes on between the ears of Mancini's players remains a mystery. City were worthy enough champions but they are not so much a team as a series of expensive one-man acts and when the juggler starts dropping things or the conjuror runs out of rabbits there is little sense of collectivity to fall back on.

This may be a passing phase but City have been found out by the Champions League and while they were landed with a devilishly difficult group it is hard to imagine United making such a fist of things.

Not so long ago the thought of the Premier League being forever dominated by the Manchester clubs plus Chelsea and Arsenal was enough to prompt a yawn. Now those days are beginning to look like a free-for-all. Chelsea's season has become a 10-month pantomime with Roman Abramovich miscast as Baron Hardup and John Terry few people's idea of Buttons. But at least they should still make the top four, unlike Arsenal whose decline is the inevitable result of selling good players and buying lesser ones.

Liverpool monopolised the old First Division from the mid-70s to the end of the 80s with only Everton providing any sort of lasting challenge. Yet Brian Clough's Nottingham Forest and Bobby Robson's Ipswich, along with QPR, Watford and Southampton all added an occasional touch of novelty to the contest which is less likely now.

More's the pity.