According to Ancelotti, Pirlo is the reason Real couldn't control the midfield, acting as decoy/bait.
http://www.football-italia.net/66101/ancelotti-unlucky-real-madrid
Ancelotti said:
Pressure on Pirlo made us open up our midfield line too much and it allowed them to find a through ball for Tevez, something that happened a lot in the first half. We preferred to give him more room to prevent that..
