A 2-2 semi-final second-leg draw with Liverpool condemned City to elimination as the Reds progressed to a Wembley meeting with Championship outfit Cardiff on February 26.
But, on a day when City were forced to accept a four-match ban for Mario Balotelli which Mancini is convinced should not have been levied, the Italian also felt his side had been wronged by two major mistakes from referee Phil Dowd.
First Mancini felt Dowd should have awarded a penalty for Charlie Adam's tackle on Edin Dzeko when the game was still goalless.
Then, after Nigel de Jong's brilliant curling effort had put City in front, Dowd did award a spot-kick for handball against Micah Richards when Daniel Agger's shot struck the visitors' skipper on the leg, then shot up onto his arm.
"It hit his leg before his arm," said Mancini, before addressing Dowd's clear indication that Richards had made the initial block with his arms raised.
"He could cut his arm off.
"It is my opinion. I didn't think it was a penalty."
Conversely, he felt Adam should have been punished.
"If you watch the game, it was a penalty on Dzeko by Adam."
All this, and Balotelli as well.
Mancini feels referee Howard Webb changed his mind over the Italian`s stamp on Tottenham`s Scott Parker, robbing him of the forward for Wednesday night's game as well as clashes with Everton, Fulham and Aston Villa.
"I hope tomorrow [Thursday] they can change tonight's [Wednesday] result because they decided about Mario after the game," said Mancini.
"The referee was there. He saw everything.
"If he felt it was correct, he should send him off during the game, not after."
Earlier on Wednesday, FA chairman David Bernstein released a statement offering his personal backing to Webb, who insisted in his report of the game that he did not see the Balotelli incident, offering an opportunity to raise the violent conduct charge.
Evidently, that cut little ice with Mancini
"Everyone watched the game," he said.
"The referee was there, 10 metres from the tackle. He could have sent Mario off at that moment, not after the game because he watched the video.
"That is easy. I can be a referee in the next game."
Mancini added the alternative was the widespread use of video technology, which has been consistently vetoed by world governing body FIFA.
"He (Webb) can't say he didn't see it. He saw everything," said Mancini.
"Now it is finished and Mario can do nothing. We lost Vinny (Kompany) for four games for nothing and now we are without Mario for four games."
Nevertheless, even after Steven Gerrard's spot-kick, City still got themselves into a position where they could have taken the game into extra-time thanks to Dzeko's close-range effort.
That the goal was cancelled out by what turned out to be a decisive strike from Craig Bellamy must have been particularly galling for Mancini, who fell out with the Welshman not long after his arrival at the club, sanctioning a loan move to hometown club Cardiff, and then, last summer, his sale to the club he supported as a boy.
"What do you want me to say to that?" said Mancini, when asked if the downturn in his personal relationship with Bellamy made the outcome of Wednesday night's encounter worse.
"I am disappointed because I didn't get to the final. What changes if Bellamy scores, or Gerrard or (Andy) Carroll?
"I am happy with the players I have got. Bellamy scored. I am also happy for him."