Mata inked terms at Old Trafford last night.
Mata said on the club's website: "I am thrilled to be joining United. I have enjoyed some very happy years at Chelsea but the time has come for a new challenge. United is the perfect place for me and I am excited at the chance I have to be part of the next phase in the club's history.
"Obviously for a player like me who is trying to score goals, assist goals and be a creative player it's going to be amazing to play with those kinds of players. Wayne Rooney, Robin van Persie, Adnan, Valencia, Chicharito, Welbeck... they are all top-level players and I will try to do the best for the team."
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