The Italian boss was insistent the spot-kick given against his side was incorrect and that Edin Dzeko should have been awarded one of his own after being tripped.
The Reds secured their place in the final with a 2-2 draw, and got their first goal from the spot after Micah Richards was penalized for handling Daniel Agger's shot.
The ball appeared to bounce off of the defender's leg on to his arm, with Mancini also insisting that his team should have had a penalty of its own for an earlier challenge on Edin Dzeko.
"We gave a good performance and scored two goals," Mancini told Sky Sports. "I don't think it was a penalty for Liverpool and we should have had a penalty [for the challenge] on Dzeko, and that changed the game. [Richards] took the ball on his leg.
"I accept that football is football. There are more important things in life. It's important that we give everything in this game, but now it's finished."
The Italian was dismissive when it was suggested that the lack of appeals by the City players contributed to referee Phil Dowd's decision not to penalize the challenge on Dzeko.
"There is a referee on the pitch, and that should be enough," he said. "It was a clear penalty, an incredible penalty. It was not a penalty against us, and afterwards we did well, and scored.
"We made some mistakes, and conceded a second, stupid goal. But now it's finished, and we can do nothing."
Mancini went on to defend his decision to start the game with three central defenders, as well as young center back Stefan Savic, who was substituted at halftime.
"We conceded only a penalty that was not a penalty," he said. "We changed it because it was 1-1, and as we thought before the game – 1-1 in the first half, and second half we change.
"Savic is young. We changed in the second half only because we needed to score another goal."