The Blues bested the Red Devils in almost every single way, and a Samuel Eto'o hat-trick was enough to bury David Moyes' troops and leave them an alarming 12 points off third place in the Premier League table.
Here, we delve into exactly why this game was won and how the Blues were able to dominate their rivals.
As the XIs for the game were announced, many fans sat with their mouths agape at just how seismic the difference in quality is between Chelsea and Manchester United is right now.
Not one of the Red Devils' XI could enjoy safe passage into Chelsea's, with perhaps only Michael Carrick strong enough to argue his stance on the subject.
While that may be without the regular world-class strike-force of Wayne Rooney and Robin van Persie, it's still a damning assessment of a team supposedly challenging for the title—if not the top four at least.
It's been said before, and it'll be said again: United need serious investment if they are to return to elite status.
The basic game plans for these two sides could not have been more different. David Moyes knew his side needed to grab three points to catch up, while Jose Mourinho knew he was sitting pretty in the top three.
As always, the Chelsea victory was founded upon extremely defensive solidarity, and as Manchester United began to run out of steam, the Blues picked them off.
Mourinho defended with six or seven at all times, with special care taken to protect full-back Cesar Azpilicueta against the two-headed monster of Antonio Valencia and Rafael.
Although the Spaniard was beaten several times, you'll note that John Terry was very rarely dragged out from his central zone. Both he and Gary Cahill sat pretty in the middle, with other players dipping in to help defend the flanks.
That set up a solid platform for the Blues to deflect forced aerial assaults with ease, and from there one ball out to Willian or Eden Hazard—who played incredibly direct football—could drag the home side 50-60 yards up the pitch in five seconds.
Attack with four, defend with six. Every time.
Manchester United started very strongly, but soon fizzled out as Chelsea came alive. Why?
Jose Mourinho made several tweaks to his system in the first 15 minutes to get his side a foothold in the game, most notably to the positioning and tendencies of David Luiz and Oscar.
Both dropped deeper than usual in the shell 4-2-3-1 setup, with Luiz anchoring the midfield from around the "D" and Oscar fishing for an early pass out of defence in his own third.
From there, Oscar in particular became integral to the Blues fighting their way out of their own half, sparking attacks and, perhaps most importantly, drifting freely to level out and balance the formation.
With the game done and dusted at 3-1, Nemanja Vidic brought joy to Sunderland fans everywhere by chopping down Eden Hazard and collecting a red card. He's now suspended for the Capital One Cup semifinal second leg.
Seconds later, Rafael committed a two-footed lunge by the sideline, and while he won the ball cleanly, he risked the wrath of the referee once again. He received a yellow card, but it's arguable it was even more deserving of a red than his teammate's challenge.
There were 44 tackles in total over the course of the 90 minutes, with United committing 21 fouls to Chelsea's 15. Whereas David Luiz was the only Blues player to be booked, United picked up three petulant cards plus the red for Vidic.
The Red Devils struggled, got frustrated and let it show.
Sometimes it comes down to who takes their chances. Football can be a cruel mistress sometimes.
There's no doubt Manchester United were the stronger side for the first 20-25 minutes, dominating the ball and creating several chances in the final third. Unfortunately, those chances created were not put away, and Chelsea's first foray up the pitch resulted in a goal in the 17th minute.
Ashley Young missed a golden chance in just the second minute after great buildup play in the box; Adnan Januzaj had an early shot blocked; Antonio Valencia hit the byline several times early on, but to no avail.
The disparity between the two teams' respective "killer" instincts was noticeable.