With seven games down in the Premier League season, the two Manchester clubs are leading the way.
City and United are level on points at the top of the league, with only goal difference putting Pep Guardiola's side ahead of Jose Mourinho's team.
Both have won six of their opening games, drawing the only one and losing none. Their closest challengers, Tottenham, are already five points behind.
The two teams don't meet in the league until December, so there's a chance one could still be undefeated going into the new year.
It's City's attack that has caught the eye of fans across England, scoring 22 goals in seven matches, but Mourinho's Red Devils have only scored one less.
Supporters of Guardiola's side may be concentrating on their world-class forwards, but followers of United have been watching a player in midfield many would describe as a 'Plan B'.
Marouane Fellaini has been featuring regularly at Old Trafford since Paul Pogba limped off injured against Basel in September.
And the Belgian has faced his fair share of criticism since moving from Everton to Manchester in 2013.
But after scoring three times in the league already this season, Ryan Giggs believes he's already repaid Mourinho's faith and has overcome his critics.
"Marouane Fellaini has really proved his importance, stepping in for Paul Pogba," Giggs told Sky Sports, per Goal.
"He has scored important goals, as he did at Everton, and I'm really pleased for him after taking a lot of stick over the years."
The Welsh legend also revealed that Fellaini is a model professional, who always impressed him in training.
"I've worked with him and he's a great lad to train because he does exactly what you want. He hasn't let the fans bother him because he's always had the support of the players and the coaches."
With Pogba out for the foreseeable future, Mourinho needed a fringe player to step up and it appears Fellaini has done just that.
As United are seriously challenging for the Premier League and Champions League this year, only time will tell if he'll be able to do enough to help his team pick up some silverware come May.
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