Vincent Kompany's winner in first-half stoppage time means that if City win their final two games - at Newcastle on Sunday and at home to QPR on the last day - they will be crowned champions for the first time since 1968.
And clearly the prospect does not please Sir Alex Ferguson, who approached opposite number Roberto Mancini in a finger-jabbing fury after Nigel de Jong had brought down Danny Welbeck in the second half.
The Italian responded in kind and at one point only fourth official Mike Jones stood between the pair, who after repeated clashes, were eventually pulled apart by their backroom staff.
Tempers had cooled at the final whistle enough for the customary handshake to take place, although the fire mattered little to City.
Just four games after that Arsenal debacle, after which their hopes appeared dead, City are back on top and agonisingly close to their holy grail after completing a league double over their great rivals for only the second time in 42 years.
Although the team sheets indicated Ferguson had adopted a cautious approach and Mancini a more attack-minded one, in fact the opening exchanges provided an alternate view.
With his midfield reinforced by the introduction of Park Ji-sung to a Premier League starting line-up for the first-time since January, Ferguson's side quickly got into their stride and looked capable of carving out a decent opportunity or two.
However, Nani wasted their clearest opportunity when he ignored Phil Jones' overlapping burst and let fly from 35 yards with a shot that was hopelessly off-target.
City meanwhile began sluggishly, their midfield seemingly incapable of stringing a succession of passes together with any regularity.
Samir Nasri was the man who sparked them into life with a couple of mazy dribbles as the hosts started to get near the byline, which always gives defences cause for concern.
Sergio Aguero screwed a volley wide, then Pablo Zabaleta seized on an opportunity he would have been better leaving for Nasri and his shot rolled through to David de Gea.
After all the hype, it was hardly a classic, although as the clock ticked down towards half-time, the United camp presumably reflected they were quite happy at that.
So, to go behind in stoppage time in such orthodox fashion would have been particularly galling for the visitors.
De Gea's frailties under the high ball are well known by now. When David Silva curled over the second of successive corners, a stronger, more confident goalkeeper might have come to punch.
Instead, he left it to his defenders.
Chris Smalling, like Park, making his first start since January after Jonny Evans was ruled out through injury, momentarily lost Kompany on their run from the edge of the box and was still marginally out of position when the Belgian rose to power home from six yards.
It was a devastating goal for United to lose as there had been no obvious indication they were likely to score.
Wayne Rooney looked particularly out of sorts, isolated up front and generally unhappy with the buffeting he was receiving, which had only drawn one yellow card for Kompany.
The second half was only 12 minutes old when Ferguson offered his star man some badly-needed support, replacing Park with Welbeck.
Immediately before the change though United might have found themselves two down when De Gea came for a corner without getting near it and Nasri ended up curling wide of the far post.
Even when the Red Devils did build some attacking momentum, their final pass was either off-target or overhit, ensuring Hart was not tested.
However, with his side well capable of grabbing a second, Mancini's decision to replace Carlos Tevez with De Jong hinted at containment, a very dangerous ploy against this particular set of opponents.
Yaya Toure did thrash a long-range effort wide, his shot close enough to have De Gea scrambling across his goal.
And, in truth, United seemed to have precious few ideas about prising their opponents open.
De Jong's foul on Welbeck brought a yellow card for the Dutchman and sparked the furious touchline row between Ferguson and Mancini. Peace was eventually restored but the visitors failed to feed off their manager's fire.
Toure came agonisingly close to grabbing a second for the Blues and De Gea made an excellent save to deny Gael Clichy.
And despite five minutes' stoppage time, the Blues cruised home, and the songs of celebration began with City two games from glory.