The City No. 1, who was visibly angered by the late defeat, claimed it was "not on" after his side’s defeat to the Spanish champions.
And despite Mancini broadly agreeing that the whole team were to blame rather than just his goalkeeper, the Italian said he was the only person who should be openly criticising his team.
"Joe Hart should stay in goal and make saves," a frustrated Mancini told reporters after the game.
"If anyone should criticise the team it should be me, not Joe Hart. I am the judge, not Joe Hart."
City looked set for a memorable win at the Santiago Bernabeu after an Aleksandar Kolarov free kick five minutes from time edged them ahead.
However, strikes from Karim Benzema and Cristiano Ronaldo - which seemed to deceive Hart - meant the English side returned home pointless from their first Champions League game of the season.
Despite being downhearted after the clash, Mancini insisted that, although it was not the start his side wanted to this season’s European campaign, there was no need to get carried away.
"We should be disappointed that we have lost this point but we can improve," he said.
"Other teams will lose here. We have five games and it is important that we beat Dortmund in the next game. It will be difficult because Dortmund are a top team."