So the balance of power has finally shifted. Manchester United have now become the noisy neighbours and their statement of intent will have been heard as far away as South Wales.
Having trailed Manchester City at the top of the Premier League for all but a few hours in February since October 15, Wayne Rooney's double against West Brom at Old Trafford yesterday proved enough to elevate United above their Mancunian rivals, who conceded top spot with a surprise 1-0 defeat at Swansea.
For a short period, Swansea's Luke Moore rivalled Rooney in the Old Trafford hero stakes thanks to his 83rd-minute goal at the Liberty Stadium which consigned City to their third defeat in eight games.
During the same period, United have won seven and drawn once to erode City's previously commanding lead and, with 10 games left to play, Alex Ferguson's men have planted their flag at the summit.
News of Moore's goal swept around Old Trafford in a tsunami of noise, chants taunting City were aired, but two decades of title challenges ought to breed caution rather than complacency and the regulars inside the stadium will know that much can be won and lost between now and the finish line.
Yes, United have what appears to be a less hazardous fixture list and, if they triumph at Wolves next Sunday, could leave City trailing by four points ahead of their testing encounter with Chelsea at the Etihad Stadium three days later.
But, while the excitable callers on MUTV's predictably one-sided post-match phone-in were ready to engrave United's name on the Premier League trophy once again, there is unlikely to be such misplaced confidence within the dressing-room.
Form is certainly on United's side, however. A seven-point swing in their favour since New Year's Day has gnawed away at City's lead and Rooney, whose output this season has been sporadic, now has nine goals in his last six appearances.
In truth, their performance against West Brom was a slow burner, with Roy Hodgson's team proving obdurate opponents in the opening half-hour.
Buoyed by three successive league wins, in which they had scored 10 goals, West Brom appeared determined to build on last season's draw at Old Trafford.
With Marc-Antoine Fortune deployed as a lone striker, the visitors defended deep, with 10 men aiming to suffocate every United attack, but Ferguson had selected an adventurous starting XI and the flair and intent of Rooney, Ashley Young, Danny Welbeck and Javier Hernandez.
Young, the two-goal hero of last Sunday's victory at Tottenham, was unplayable, nut-megging the forlorn full-back Gabrial Tamas and peppering the Albion penalty area with crosses.
Chances went begging, however, and United lived dangerously, with Keith Andrews and Chris Brunt going close for Hodgson's team before Rooney opened the scoring after 35 minutes.
The goal was sparked by Paul Scholes' pass to Hernandez on the edge of the penalty area, prompting the Mexican forward to cut inside Liam Ridgewell before aiming a left-foot shot goalwards from just inside the 18-yard box.
Hernandez's effort appeared to heading wide but, always aware, Rooney darted ahead of the Albion centre-halves before directing the ball past goalkeeper Ben Foster with his outstretched left leg.
Initial suspicions that Rooney had strayed offside were dismissed with television replays showing that the England forward had timed his run to perfection.
West Brom reacted by increasing their bite in the tackle and Young and Welbeck were on the wrong end of heavy challenges by Tamas and James Morrison.
The rough-house approach continued early in the second half, with defender Jonas Olsson being booked by referee Lee Probert for a shove on Rooney.
It proved to be a costly caution for the Albion centre-half, with Probert sending him off for a second booking after 66 minutes following a crude challenge from behind on Welbeck.
A goal down and a man down, West Brom were now facing a United onslaught and Foster was forced into a series of saves to repel his former Old Trafford team-mates.
But United were given the opportunity to double their lead when Probert pointed to the penalty spot in the 70th minute following a foul by Andrews on Young.
Rooney placed the ball on the spot and coolly sent Foster the wrong way to score his 20th league goal of the season and 26th in all competitions.
Two years after netting 34 goals in his most productive season for United, Rooney is now within sight of surpassing that tally. He is also now just eight goals short of passing George Best and Dennis Viollet to move to fourth in the club's all-time scoring charts.
If Rooney passes those personal milestones, it will only add fuel to United's push for the title.
And while City must now negotiate a daunting fixture list, which includes Chelsea and Arsenal, before they lock horns with United at the Etihad on April 30, Ferguson's men will tackle five of the bottom six. (© Daily Telegraph, London)