United, who finalised a club record deal to sign Mata from Chelsea on Saturda evening, also need reinforcements in defence and a new commanding force in midfield.
Clearly matters need to improve at United sooner rather than later and Mata's imminent arrival, for £37 million, is a significant step in the right direction.
In time it could be seen to represent the real start of manager David Moyes's United and the launching of a new era following Alex Ferguson's retirement at the end of last season after 27 years at the helm.
Other arrivals should come later this year with the careers of long-serving players like Ryan Giggs, Rio Ferdinand, Nemanja Vidic and Patrice Evra coming to a close.
The Mata transfer also casts doubt on the future of Japan playmaker Shinji Kagawa who joined United from Borussia Dortmund 18 months ago but has never fully established himself at Old Trafford.
The 25-year-old Mata, who scored 32 goals in 135 appearances for Chelsea after joining from Valencia for £23.5 million pounds in August 2011, succeeds Bulgarian Dimitar Berbatov as United's record signing - but holding that distinction is no guarantee of success.
On the surface Berbatov appears to have done reasonably well at United with 56 goals in 149 games but in reality he never quite lived up to expectations and in August 2012 Ferguson sold him to Premier League rivals Fulham after four seasons with the club.
Mata is a totally different type of player and United are set to acquire a clever attacking midfielder with an eye for goal and the ability to change a game with a shrewd pass or a shimmy or a feint.
United have lacked flair this season. The Spaniard should offer creativity playing behind the front men and, if he is given a free role, will add some much-needed unpredictability.
Striking up an immediate understanding with a fully-fit Van Persie and Rooney will be essential although Mata will also need to be complimented by a robust presence in midfield - a position once occupied by former hard-man captain Roy Keane.
Mata was the darling of the Stamford Bridge crowd, having been voted Player of the Year when Chelsea won the Champions League in 2011-12 and again last season when they won the Europa League.
However, his days seemed to be numbered as soon as Jose Mourinho returned in the close season for a second stint in charge.
As far as the Portuguese was concerned Mata did not have the necessary pace or tackling ability to provide the defensive barrier he craves from his attacking midfielders when they lose possession of the ball.
Preferring Brazilians Oscar and Willian and Belgian Eden Hazard in the three creative roles behind the sole striker in Chelsea's 4-2-3-1 system, Mourinho's team have won six games in a row in all competitions and are only two points behind Arsenal at the top of the league.
Mata needs to play regularly with the World Cup in Brazil coming up in June and he will walk into a United team crying out for salvation after a miserable first six months under Moyes that has lurched from one low point to another.
There was an almost surreal atmosphere at Old Trafford on Wednesday when they lost their League Cup semi-final to Sunderland on penalties.
The only thing that softened the blow was the news of Mata's impending arrival.
United still have the financial clout, the glamour, the appeal and the potential to attract the world's best players even if the unthinkable happens and they fail to qualify for next season's Champions League.
Moyes will be hoping the big-money Mata deal provides the same kind of spark that Germany playmaker Mesut Ozil brought to Arsenal when he joined the club at the start of the season.
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