David Moyes hasn't had many comfortable nights as manager of Manchester United.
He picked Mata, his new £37.1 million buy, from the start against Cardiff, but it was perhaps a bigger boost that he could name both Rooney and Van Persie in his squad.
Of the eight games Van Persie and Rooney have started together this season, United have won six. You suspect that if they had both stayed fit this season, United wouldn't be languishing down in seventh in the Premier League table.
Moyes started with Mata behind Van Persie. And when Rooney came off the bench in the second half, it was Van Persie who went off.
It leaves unresolved the issue of where the Spaniard is going to play when both Rooney and Van Persie are fit.
Moyes, and Sir Alex Ferguson before him, have faced a similar problem with Shinji Kagawa.
Kagawa is more comfortable playing behind a striker. But with Moyes preferring to play with a front two, the Japanese midfielder has found most of his opportunities come on the left of midfield.
Mata, too, is more comfortable playing centrally. He looked neat and tidy in the hole behind Van Persie against Cardiff, but there is a question mark over how many times he will get to play there.
If Moyes wants to stick with his variation of 4-4-2, the obvious solution is to play Van Persie and Rooney as a pair with Mata out wide.
And when you add in Adnan Januzaj—probably United's best player so far this season—playing on the other side, it could leave Moyes' team looking very narrow.
Both Mata and Januzaj will naturally want to drift inside, putting a lot of pressure on the full-backs to supply the width.
Trying to fit in Van Persie, Rooney and Mata isn't a bad problem to have. Mata's arrival from Chelsea will, at the very least, make United more creative—something they've lacked this season.
But it's still a dilemma Moyes has to solve. He kept his cards close to his chest on Tuesday night, never having more than two of them on the pitch at the same time.
A trip to Stoke City and the Britannia Stadium on Saturday offers the next chance to get an insight into Moyes' long-term thinking.
Until then, at least he can sleep a little more comfortably.
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