The all-Manchester clash was secured on Sunday after Micah Richards headed home a David Silva corner against Reading. The right-back's 74th minute goal ensured the sides will meet at the last-four stage of the competition for the first time since 1926.
Speaking to reporters after the match, the Italian stated he would treat the tie as any other despite the mouthwatering draw.
He said: "In football, every year you can meet your [closest] opponents two-times minimum, or three or four.
"For me, it is a great semi-final. I like this.
"We know that when we arrive in the semi-final, it is always hard."
City fell to United at the same stage of the League Cup last term and Wayne Rooney's dramatic overheard kick saw them condemned to a 2-1 defeat in the Premier League last month. Mancini reiterated that such results weren't important and echoed earlier statements that City are "now very close" to Sir Alex Ferguson's decorated squad.
The 46-year-old continued: "I think for us it was important to win against Reading. After, it is not important which team we meet in the semi-final or final.
He added: "I think for us, it is important to improve. We have improved a lot from the last year.
"We are a good team, and also, when we lost the game, we played as a team. That is important.
"You can improve only when you have lost you understand which mistakes you did. I think that Manchester City now is very close to this club [Manchester United]."
City laboured at times against their Championship opponents but pressed to rebound from Thursday's 2-0 Europa League loss to Dynamo Kiev. Mancini blamed fixture congestion for City's display and stated his delight at helping to secure a trip to Wembley for the City support.
He said: "Three days ago, [there was] a hard match [against Dynamo Kiev], today, hard match.
"It is normal when you play every three days you have four or five players injured. In this moment, it is very hard.
"For today, I am very happy for the supporters because they deserve to go to Wembley for this game."