The Premier League champion twice held the lead before falling to a shock 4-2 defeat to Aston Villa in the League Cup third round at the Etihad Stadium
The hosts twice got themselves in front only to be pulled level on both occasions, before extra time goals from Gabriel Agbonlahor and Charles N'Zogbia gave the Villans a shock win.
Mancini had recently seen his side surrender a lead late on against Real Madrid in the Champions League and underlined his concern at the worrying trend.
"This [conceding goals and throwing away leads] is a problem, we need to work with our defenders because they are not working well at this moment," he told reporters. "I am disappointed for the result. I think it was a difficult match because Aston Villa are a good team, we didn’t play well. We had one unlucky moment because we had chance to score but conceded a goal.
"I think we made some mistakes with their goals, but at the end of the day they deserved to go through. We didn’t play well, and our play is not quick. We want to take a touch more every time."
The Italian also hit out at opposition manager Paul Lambert after the Scot angrily reacted to his opposite number calling for a Villa player to be booked.
"I am tired of this manager because I didn’t say nothing to him, I only asked [the fourth official] if it was a yellow card without moving my hands," he added. "And sometime after this manager goes to a big stadium and the other manager doesn’t say anything and they don’t say nothing. I am tired of it, very tired."
Lambert on the other hand was delighted with the victory, saying: "It’s a massive result for us, really huge.
"I think we never deserved to go a goal behind but we did well to come from behind, not just once but twice and to go and win the game is a huge effort for us. I’m delighted with the way we played."
After being told what Mancini had said regarding their clash, the 43-year-old replied: "If that’s what he said [that he was just talking to the fourth official] then fine, I respect him as a manager and as an ex-player. I don’t have a problem [with him]."
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