The problem with Rondo's performance was that when the team needed to execute it's offense, it couldn't. He was only one of several guys who contributed to that, but he's the point guard, so it is particularly important for him to get the ball to the right people in the right places. He failed. The lobs were dangerous, but didn't result in turnovers. The location and slowness of where he got the ball to Pierce and Garnett was the problem. The offense was pushed out and the defender was able to lock down on the ball before the ball got there.
Rondo is one of the guys who can break the defense down and he has a big opportunity with Billups being injured. He has to make things easier for the others.