Having battled with the Red Devils for supremacy over the past decade, the Blues currently have the advantage with Antonio Conte as manager - while Jose Mourinho is at United.
As we know, Chelsea sacked Mourinho last season following an awful start and now appear to be much better off with Conte at the helm.
They also have bragging rights where recent results are concerned. Back in October, Chelsea thrashed United 4-0 at Stamford Bridge after Pedro scored within 29 seconds.
All this sets up an exciting encounter on Monday, with United aiming to progress into the FA Cup semi-finals and defend their title.
But the odds of that happening are slim. Chelsea are in fantastic form at the moment and haven't lost at home since September's 2-1 defeat against Liverpool.
United will be all too aware of the fact they're technically underdogs but that hasn't stopped Chelsea from trying to play some mind games.
In a pre-match review on their official website, the Blues have mocked the fact their opponents haven't moved from sixth in 143 days - a Premier League record (see below).
CHELSEA TROLL MAN UTD
Hilariously, they wrote: "Monday's cup opponents are enjoying a long unbeaten run in the league stretching back to October.
"It has lifted them all the way from sixth to sixth.
"That last defeat was, of course, the one they endured at the Bridge. Pedro’s 29.6 seconds opener in that 4-0 triumph remains the fastest goal in the league this season."
A genuine mistake or a blatant attempt to troll United? I'll let you decide that one for yourselves.
Whatever the reason, the Red Devils will be even more fired up for the game as they chase their second domestic title of the season.
Having won the EFL Cup late last month, Mourinho is on course for a promising first term in charge at the Theatre of Dreams, especially with the top four still in sight.
But Chelsea look unbeatable at the moment and it'll take some doing to knock them out of the FA Cup at Stamford Bridge.
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