Dida is still receiving great criticism across Europe for his theatrics at the end of Milan's Champions League defeat at Celtic.
"Over the years Dida has shown himself to be a very professional and sporting athlete, who even got back up after he was hit by a firework," said Ancelotti, referring to the 2005 Champions League quarter-final against Inter.
"The other night he made a mistake. I don't know why he did it, but considering his history of good behaviour we should put it all behind us. It was a mistake, that's all there is to say."
Dida collapsed to the ground after a fan ran on to the pitch and tapped him lightly on the cheek, but the Brazilian went off on a stretcher clutching an ice-pack to his face and could now be suspended by UEFA for simulation.
"The fact he went off the field was an evaluation by the medical staff. They did not see the incident in real time and could not know the extent of the damage, so they preferred to avoid any potential risks."
Even before those histrionics, Dida had been continually insulted by the Rossoneri supporters and the media highlighted his errors in both Celtic goals.
"Dida has not made many mistakes," insisted Ancelotti. "There was one at Siena, but in Glasgow we took a different view. We believe his vision was impaired by the other players in front of him, so he didn't see the shot until late. You can make your own evaluations, we will make ours."