It was too good an opportunity to miss. As David Moyes was busy writing out a cheque for a club record £37 million, Mourinho was taking responsibility for Mata's shortcomings.
In the way you might apologise to a blind date for finding them so unattractive you have to cut the evening short, Mourinho apologised to Mata for deciding the World Cup winner was not good enough to fit into his system at Stamford Bridge.
Maybe that made him, as a man, as a player, stronger but I gave him nothing to be honest and I feel sorry with that.
I tried to make him play in a position where he was not comfortable. He gave everything and played some good matches in that position.
We are speaking about a world champion, a European champion. It is difficult for him.
I feel sorry for that and because of that I feel we couldn't stop him going to Manchester United, despite being Manchester United's direct rival.
But as well as an apology to Mata, it was also a veiled warning to United and Moyes.
Had Mourinho chosen to get straight to the point instead, he could quite easily have said "Mata cannot play wide."
That was, after all, the reason Chelsea agreed to let their two-time Player of the Year leave. Mourinho decided Oscar was his No.10 which left Mata with three options. Learn to play in a new position, sit on the bench or pack your bags.
He chose the third.
But there were few who thought Mata's prospects were any brighter at Old Trafford. Mourinho, it would seem, included.
With Robin van Persie and Wayne Rooney in the squad, it was difficult to see how Moyes could accommodate Mata without playing him wide. It was the same problem Sir Alex Ferguson faced with Shinji Kagawa last season.
And Mourinho, for the most part, has been proved right.
Mata has played on the left and the right. But, with Van Persie and Rooney available, never centrally. That is, until now.
It is difficult to argue that United are better off now that Van Persie has been ruled out for six weeks with a knee injury. He's too good a player for that to be true.
But it has made Moyes' job a little bit easier. Against West Ham at Upton Park, he was free to bring Mata in from the shadows to play behind Rooney.
And it was no coincidence that Mata responded with the most impressive performance of his short United career.
It is something Moyes has stumbled on. It is unlikely he would have dropped Van Persie or Rooney for Mata's benefit. But the former Valencia midfielder is set to benefit from the Dutchman's absence.
And, in a roundabout way, so can United.
Mata will start behind Rooney again on Tuesday when Manchester City visit Old Trafford.
It will be a more balanced United side. One built around Mata's creation and invention in the space between the forwards and the midfield.
It will be one with a chance of pulling off a result that seemed unlikely barely a week ago. One with a chance of salvaging some respectability from this season. Even with Van Persie forced to watch from the stands.