The biggest story to emerge from Stamford Bridge during the transfer window was a departure rather than an arrival.
Such a move would have been unthinkable even six months ago, but it could prove to be an inspired piece of man-management by Jose Mourinho.
The "Special One" has made no secret of his intention to build his Chelsea side around Oscar, and selling Mata was a statement of Mourinho's intent as much as it was a display of absolute faith in the Brazilian youngster. Matt McGeehan of The Independent reports:
Another thing is to adapt to the way we want to play. In this moment, Oscar is my No. 10 and, if somebody tells me that Oscar is not Chelsea's best player since the beginning of the season, I'd have to disagree.
Many column inches were written expressing shock at Mourinho's preference for Oscar over Mata, but such an outcome was always likely.
Mourinho's comments on the defensive tactics of Sam Allardyce's West Ham side drew bemusement from many, as per Sky Sports. A fine manager no doubt, but Mourinho is no stranger to the dark arts and will play the pragmatist when facing a technically superior side.
There is no finer example than his Inter Milan side, which beat Barcelona on their run to Champions League glory.
And that is where Oscar comes in.
Mourinho loves a grafter. And the boy from Sao Paulo, despite his formidable repertoire of skills, is a grafter.
Against West Ham in November, he put in eight tackles, winning six of them, as per eplindex.com.
Fine players have seen themselves sidelined because they didn't fit into Mourinho's system. Joe Cole was chastised for his failure to track back, as Oliver Holt of The Mirror wrote.
Mata is the latest in a list of players sidelined to help Mourinho achieve his masterplan.
And the move will prove a key and canny piece of man-management. Mourinho thrives on engendering tremendous loyalty from his players. What greater nod of approval could Oscar have received than being favoured over Chelsea's reigning player of the year.
The furore surrounding the Mata transfer overshadowed some astute pieces of business by Chelsea.
Stamford Bridge welcomed Mohamed Salah from Basel for £11 million. The lightning-quick Egyptian winger had looked set for a move to Liverpool, as reports Andy Hunter of The Guardian, but Chelsea snuck in to secure his signature.
Earlier in the window, Mourinho had welcomed Nemanja Matic back to west London for £21 million, and he also made a late swoop for St Etienne's Kurt Zouma, who will stay on loan at the French club until the end of the season.
Chelsea's shrewdest piece of business this January, however, was the sale of Mata. And the proof will be in the development of Oscar.