A second-half goal from Demba Ba was the difference on the night as a fresher-looking Chelsea simply outplayed and out-defended their opponents, who didn't look like the cohesive, attacking unit that they've been throughout the Premier League all year.
The win saw the Blues' incredible FA Cup streak continue, and has them primed to repeat on their 2012 success if they can get past the Citizens.
For the Red Devils, however, the loss ends their chance at the league-cup double in 2013 and leaves them with just the one trophy to their name this year.
What were the biggest talking points from the Blues' gritty 1-0 win over United in the Cup? Read on and find out.
United's Squad Depth is Remarkable
The squad that Manchester United ran out against Chelsea, in what was arguably their biggest remaining game this season (given that the title is essentially won), was truly quite incredible.
There was no Wayne Rooney or Nemanja Vidic. Robin van Persie started from the bench, as did Ashley Young and Shinji Kagawa. Antonio Valencia started the game at right-back instead of Rafael Da Silva and Phil Jones played his part as a central defensive midfielder.
Whilst there were injuries and the like that forced these changes, the reality was that this team was such a far cry from the what we'd expected. It was such a different side to that which had tore up the Premier League and Champions League through 2013, and yet, it very nearly won.
Were it not for a moment of brilliance from Demba Ba (which we'll get to in a minute), the Red Devils' second-string squad could nearly have won this one.
Few teams in the world boast depth like this, and few teams would have been capable of mixing it with Chelsea's full-strength team on their home ground.
Demba Ba and Petr Cech Were Just too Good
As good as United were defensively, Petr Cech was better. And as good as United were going forward, Chelsea striker Demba Ba was better again.
We start with Ba, whose instinctive finish over David De Gea turned out to be the game-winning goal—and deservedly so, given the raw talent it showed. Ba was played through thanks to a lovely ball from Juan Mata. With very little room to operate, the striker's ability to lob over David de Gea, despite being at full stretch, showed just how good the Senegalese striker is.
1-0 to Chelsea, all thanks to that brilliant effort, and that lead was preserved by Cech in the second half with an incredible reflex save at short range.
Manchester United striker Javier Hernandez was only a few yards away from Cech's goal when his header came in—an attempt to go back behind him, with Cech scrambling across his goal. However, Cech instinctively stuck out his left hand and tipped the ball over the bar—perhaps the defining moment of the half as the Blues defended gallantly.
He had almost no right to make the save that he did, and yet he somehow managed to keep a clean sheet for Chelsea that would ultimately win them the game.
Two individual moments of brilliance had ended United's dream of the double.
United Paid the Price for Not Resting Players
But perhaps the biggest storyline and talking point to emerge from this one was the fact that United paid the price for not resting their players on the weekend.
United fielded a very strong team against Sunderland in the Premier League despite having a huge lead in the title race. They started Kagawa, Van Persie, Vidic and Young—all of whom were therefore missing from their game just two days later against Chelsea.
The Blues, on the other hand, rested a number of players against Southampton on the weekend—losing 2-1 to the lowly Saints as a result—but saw those rested players really come to the fore as they triumphed over the Red Devils in the cup.
Chelsea left Ba, Mata, David Luiz, Eden Hazard and Ashley Cole out of their starting lineup last week, and those stars all shined here. In particular were Ba and Mata, whose attacking creativity saw the only goal of the game and kept Chelsea's incredible FA Cup run alive.
One must wonder how United would have fared in this one had Van Persie, Kagawa, Young and Vidic all been rested on the weekend and thus played here. We'll never know for sure, but you can guarantee it would have been a better performance against Chelsea if they had.
In the end, United paid the ultimate price for not resting their stars—beaten by their rivals, knocked out of the cup and saw their chance at the double slip away.
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