The gulf between the two Manchester clubs was at its most stark in the English Premier League on Saturday.
A few hours after United's latest disjointed display in a 1-1 draw at home to Southampton, City coped just fine with resting key players in a 4-0 win at Norwich - led by a hat trick from Raheem Sterling - that extended its lead to 12 points.
Last season, City and United finished as the top two. This season, they are separated by 23 points with a third of the season still to play and United in fifth place.
How crucial might that day be, at the end of last August, when United beat City to the signature of Cristiano Ronaldo? Some regarded that as a statement signing that could tip the balance of power United's way.
Six months later and Ronaldo is on his worst scoring run in 13 years - he hasn't found the net in his last six games - and City has just risen to the top of the league's scoring charts on 61 goals, without a recognized striker in its squad.
Who needs one when City has so many attacking midfielders capable of scoring? Against Norwich, Sterling scored either side of Phil Foden and then his third goal from a rebound off his saved penalty to move on to 10 in the league, making him City's leading scorer.
City manager Pep Guardiola didn't even need to bring the likes of Kevin De Bruyne or Joao Cancelo off the bench, keeping them fresh for Sporting in the Champions League on Tuesday.
Second-placed Liverpool has two games in hand over City, starting away to last-placed Burnley on Sunday.
As for United, Ralf Rangnick is finding it as hard to get a tune out of the team as Ole Gunnar Solskjaer did. The latest problem is hanging onto a lead, with Che Adams' 48th-minute goal for Southampton canceling out Jadon Sancho's opener for United in the 21st.
United also led at halftime in its 1-1 draw with Burnley on Tuesday and, before that, its FA Cup match against second-tier Middlesbrough that United ended up losing on penalties.
Rangnick is struggling to work out why his team collapses after halftime, but he needs to fix the problem quickly.
United remained one spot outside the Champions League places, with Arsenal and Tottenham - the teams in sixth and seventh - having two and three games in hand, respectively.
EVERTON'S BIG WIN
Scoring goals isn't proving a problem for Everton in the early days of Frank Lampard's tenure.
Make that seven goals in two home games under Lampard after Everton beat Leeds 3-0 thanks to scores by Seamus Coleman, Michael Keane and Anthony Gordon. Last weekend, Everton defeated Brentford 4-1 in the FA Cup.
Everton has been in freefall in the league but a second win since September lifted the team five points clear of the relegation zone - and within a point of Marcelo Bielsa's Leeds.
HODGSON'S BAD START
The arrival of Roy Hodgson has done nothing to improve Watford's fortunes.
A 2-0 loss to Brighton was Watford's sixth successive home defeat - a first for the club in the top division.
Since replacing Claudio Ranieri, the 74-year-old Hodgson hasn't seen his new team score. There was also a 0-0 draw at last-placed Burnley and a 1-0 loss at West Ham.
Watford stayed in next-to-last place, one point ahead of a Burnley team that has played three games fewer.
CHEERS FOR ERIKSEN
Christian Eriksen wasn't ready to make his debut for Brentford in the 0-0 draw against Crystal Palace. That didn't stop him getting the biggest cheer of the match.
The Denmark international was introduced to the team's supporters on the field ahead of kickoff, eight months to the day since his cardiac arrest at the European Championship.
Eriksen, who has signed a six-month deal with Brentford, is expected to play in a behind-closed-doors friendly on Monday before a potential debut at Arsenal next Saturday.
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