Rafa had a big impact on Juan Mata last season utilizing his strengths very well. He played him as a proper number 10 (not just in position) compared to his predecessor but understood the subtlety of his play as well (I still recall him shifting Mata to the left of a 4-4-2 won Chelsea the game against United).
Mata under Rafa doubled his figures compared to the season before:
Goals/Assists (all comps)= 2011-2012 (12/13) - 2012-2013 (20/35)
Of course Mata had an amazing season, but pundits complained of how his central position weakened Chelsea in midfield. How will Mourinho see it? He had a lot of friction with Ozil (many videos on youtube) but still put his faith in him until the very end.
Enough of that though, I'm sure you lot would rather watch the game than hear me ramble.