One of the things I've noticed this season is that previously, let's say with the Alonso/Mascherano partnership, the roles in the centre were very clearly defined. Put simply, Masch won the ball back and Alonso distributed it (though Alonso did gradually improve his tackling ability!).
What was brilliant though is that Masch tracked back through the centre but also on the flanks allowing the wingers to remain higher up the pitch. The other important point is that Masch never gave up when tracking back i.e. HE took responsibility for the attacking player with the ball and didn't give up until he won it back, again leaving the defenders better covered.
This season what I've found is that Lucas, a different type of player (all round far less limited than Masch), has a tendency to track the attacking player up to a point and then peel off and (in theory allow the defenders to take over) generally this creates holes and spaces for the opposition.
