When he saw the 2 CB's mindlessly charge forward he should perhaps have had the awareness to step out to play Ruiz off side.
Saying that, it was two quality incisive passes from Hangeland & Dempsey.
You'll see from the link below that the question's more why did he drift away from Ruiz so much in the penalty area. If he'd stayed tighter he would've at least put pressure on him & perhaps even have blocked it if he really throws himself across it (although few of them seem willing to put their body on the line at the moment).
I feel a bit sorry for him as its a tough situation to come in to with the team playing so badly & he hasn't played much in the Premiership. He would at least expect a bit of leadership to help him out from Cahill or Knight but there was little to be seen. He'll get better the more he plays & the better the team plays (hopefully).
http://www.youtube.com/watch?v=2kNi9ukVnA4