The Premier League champions cruised to a 6-0 thrashing of Ipswich on Sunday afternoon.
Phil Foden scored twice, while goals from Mateo Kovacic, Jeremy Doku, Erling Haaland and James McAtee helped the visitors maintain their upturn in form.
It is the 13th time City have scored six or more goals in the Premier League under Pep Guardiola.
That tally draws the Spaniard level with Arsene Wenger at Arsenal and he is now just one behind Sir Alex Ferguson's record as United boss.
City's comfortable victory came just a couple of hours after another defeat for their bitter rivals.
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With City already in control at Portman Road shortly after the start of the second half, the travelling fans could be heard taking aim at the Red Devils.
Chants of 'you're going down with United' were sang towards the hosts after Doku stroked in a fourth for his side.
Meanwhile, 'City's staying up' also rang around the away end as supporters made light of their own struggles this term.
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Guardiola's side endured a run of one win in 13 matches across all competitions earlier in the campaign.
However, City's latest win has extended their unbeaten run to six and lifted the champions back into the top four.
There is no such good fortune for United, though, although a first relegation since 1974 remains unlikely.
The defeat to Brighton leaves the Red Devils 13th in the table after a tenth loss from 22 league matches.
With a ten-point gap to the bottom three, however, they are closer to the drop zone than the top four, which is 12 points away from their grasp.
As four City, their win sees them leapfrog Newcastle into fourth place on goal difference.
The champions remain 12 points adrift of league leaders Liverpool, who have a game in hand on those below them.
Both City and United are in European action in midweek before their attention returns to the Premier League.
Darts World Champion Luke Littler serenaded by the Manchester United fans at Old Trafford as he shows off his trophy
The Red Devils host Rangers in the Europa League on Thursday night.
Beforehand, City travel to France to face Paris Saint-Germain in their penultimate Champions League league phase fixture on Wednesday.