Mancini clashed with Liverpool captain Steven Gerrard after the final whistle over the incident, and remained adamant that Johnson deserved more punishment, with not even a free kick awarded by referee Lee Mason.
"It was worse," Mancini claimed following the match. "This tackle was worse. Gerrard came to me and said I said something.
"It was not for Johnson. It is for the tackle. This tackle was worse than Vinny's. Everyone can see it."
The 47-year-old Italian went on to dismiss Gerrard's accusations of hypocrisy, with the England midfielder noting Mancini had been critical of what he perceived to be an attempt by Wayne Rooney to get Kompany sent off in the FA Cup tie at the Etihad Stadium.
"Steven Gerrard can say what he wants," Mancini said. "I said what I think. That is what I am used to doing.
"It is not important what Steven Gerrard or the other players have said."
Mancini admitted January could be a pivotal month for his side, with two straight losses recorded in the absence of the likes of Yaya Toure, Vincent Kompany and David Silva for one or both of the fixtures.
"We have just played two difficult games," he said.
"I knew this before, when I said that January will be an important month for us because we lose three or four important players."
The former Inter manager was unconcerned by the performance of young defender Stefan Savic, who conceded the decisive penalty in only his seventh start for the club.
"Savic needs to get experience," Mancini said.
"It is normal. He is young. Against a striker like [Andy] Carroll maybe he could have some difficulties. But in the second half it went better."
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