Mancini's side have another opportunity to redress the balance slightly after Micah Richards' 73rd-minute winner allowed them to stride past Reading and book a last-four meeting with Sir Alex Ferguson's men at Wembley on April 16 or 17.
But the Italian insists it will be next season before big-spending City can really regard themselves as United's equals and he said: "It is a great semi-final. You could see what it meant to the fans at the end. We are very close with all the top squads but we need to improve more and maybe next year we will be at the same level."
He added: "But it is important that we played a good game at Old Trafford last time and we have a chance to win, like them."
In Mancini's short time at City alone, the Blues have suffered four agonising defeats to the men from Old Trafford, the latest coming last month when Wayne Rooney's wonder goal settled matters.
Mancini made no attempt to prevent his side learning the draw before they kicked-off against Reading as, in his mind, the whole issue was irrelevant until City had overcome an obdurate Reading outfit, who proved difficult to break down.
"We knew the draw before the game but we had to win before we could think about the semi-final," said Mancini. "We are not fresh or 100% at this moment but we deserved to win. We had 17 attempts on goal."
Now United await, with Mancini insisting there is no element of revenge, even though City's first semi-final appearance in 30 years could be the prelude to a first trophy since 1976.
Mancini is preferring instead to focus on Thursday's Europa League return against Dynamo Kiev, when City will look to overturn a two-goal deficit.
"Revenge is the wrong word," he said. "Every year in football you can meet your opponent, two times minimum, maybe three of four. And before that we have important games, Kiev on Thursday, Chelsea on Sunday, after that Sunderland. We are happy for everyone but we have two more games to play before we can win the FA Cup."
Source: PA
Source: PA