Roma had been leading through Jeremy Menez's opener before Milan won a debatable penalty after Nicolas Burdisso's clash with Alessandro Nesta. Ronaldinho converted the spot-kick before laying on the winner for Alexandre Pato.
"The whole thing was a disgrace. We were playing very well and should've finished it off in the first half, we certainly had the chances to," blasted Ranieri.
"In the second half we waited a bit too long. I really hope the penalty on Ronaldinho was valid, because there were a couple we should've had too. I don't believe [Massimo] Ambrosini should've been sent off either, so the referee had a bad night.
"Looking at the footage, it looks as if Burdisso got the ball. It's difficult to tell, but the ball clearly changes direction."
Ranieri also claimed that Roma should have been awarded a spot-kick for a first half foul.
"As for the one on Menez, Thiago Silva clearly hauls him back by the shoulder. I don't know where the referee was positioned, but Thiago did a very smart foul there and it might've been difficult to spot from that angle.
"Why didn't we win? The whole world saw it, that was very clear and I need say nothing more. The referee can have a bad night, it happens, and next time he'll do better. There's no anger."