And the Red Devils' capture of the midfield maestro should prove to be the catalyst that sends them into the Champions League positions.
It is demonstrative of how far Jose Mourinho's opinion of United has fallen that he was prepared to sell Mata to last year's champions. Mourinho no longer considers David Moyes' team a threat.
BBC Sport reported that Mourinho did not want to lose Mata, however:
These are decisions a manager has to make, but for me it was a hard decision. I'd love to have him in my squad, absolutely.
But to have a player in this situation is hard. He deserves that Chelsea open the door for him.
I like people to be happy. I'm so sorry I couldn't make him happy in this squad - I'm so sad with that, but I build my team around Oscar playing as my number 10.
Since the retirement of Paul Scholes' last season, the fans at Old Trafford have called for a midfielder capable of dictating their play. In Mata, they have that man.
United's 3-1 demolition by Chelsea highlighted an ineffectual midfield that was overrun at will.
With the exception of the underrated Michael Carrick, they have lacked a calming influence who will orchestrate and supply their many attacking talents.
A positive change in the team's mood was palpable as Mata made his debut against Cardiff in a 2-0 victory on 28 January.
£37 million? A small price to pay for long-term financial security.
The much-maligned Anderson was the player to make way for Mata, as the Brazilian signed for Fiorentina on loan.
Bought to great fanfare for a combined £30 million with Nani in 2007, Anderson, 25, has struggled to make a lasting impression at Old Trafford.
Making only three starts this campaign under Moyes, BBC Sport's Phil McNulty said that few at Old Trafford would mourn the departure of Anderson.
Among the other big-name loanees from United were Federico Macheda and Wilfried Zaha.
Zaha has found first-team opportunities hard to come by since his big-money move from Crystal Palace in the summer.
Can Manchester United qualify for the Champions League after signing Juan Mata?
Macheda heads to Birmingham City for the rest of the season.
Patience was not so abundant for Fabio da Silva, though. The Brazilian full-back made a permanent switch to Cardiff.
But for the Old Trafford faithful, it will be the acquisition of Mata, a midfielder of proven quality, that will kick-start their season.