A polemic decision given Xabi's status as a star and idol at Santiago Bernabeu, there is a simple truth behind my reasoning: Nuri Sahin might be a better player and compose a more dynamic midfield with Khedira and Özil than Xabi Alonso ever will.
Alonso sometimes shies away from going forward and prefers to sit back in a deep lying playmaker stance. This makes him a little bit of a difficult player to fit into a system because he isn't great at either defending or attacking football and needs to be paired with one (or two when paired with Gerard and Mascherano at Liverpool) midfielders that complement his style.
Nuri doesn't need to be complemented, and like Khedira is more of a box-to-box midfielder that can both attack all over the field and press defensively to get the ball back.
Think of it as a midfield that might look a lot like what Germany had in the FIFA World Cup with Schweinsteiger, Khedira and Özil.
And in Sahin, Mourinho just might have found the replica of Schweinsteiger he needed for Los Merengues' midfield to work to its maximum potential.