I'm in two minds over this one. Both arguments make lots of sense.
On one hand Mata should play because his ball retention will be essential away from home. He'll feel confident and deserves the nod based on yesterday's performance. Plus, playing him means that we could use Di Maria as a means of running at a tired defence in the second half.
On the other hand Di Maria's pace will be a great help on the counter and he has it in him to roast whoever plays on that left side of their defence. He actually had a good game against Arsenal going forward prior to the red card and I'd fancy him to run the rings around Sakho, or hopefully Lovren, if given the nod.
We've got a similar predicament with Shaw and Blind, too. Do we go with the faster players that are better suited to an away game, or the slower ones that will perform better with the ball?
Decisions, decisions.
Personally, I think I'd go with Di Maria and Blind.