The champions had to settle for a third draw from five games in a 1-1 stalemate with Arsenal at the Etihad Stadium after Laurent Koscielny equalised eight minutes from time. City took the lead in the 40th minute with a header from Joleon Lescott but were flattered by it and a point was the least the visitors deserved.
The game came five days after City suffered a last-gasp defeat by Real Madrid in their opening Champions League game, leaving Mancini less than happy. He said: "I'm very sorry today for the players because it was difficult after Madrid but I'm worried because we conceded a goal. We need to improve and we need to work."
Mancini added: "In the last four games we've conceded three goals from set-pieces. This can't happen. I'm frustrated but the players are frustrated about this. If you want to win, clean sheets are important."
The result left City in seventh, four points behind leaders Chelsea and three adrift of Manchester United, and Mancini urged his team to forget about last season.
He said: "What we did has finished, it's history. Now we are like all the other teams and I don't like that we drew three games. Probably we're missing two points, from the game against Stoke maybe."
Arsene Wenger felt Arsenal were unfortunate not to get more than a point but took great heart from the performance of his side, who again showed the pre-season doom-mongers may have been overly pessimistic.
The Frenchman said: "I'm pleased because I feel it was the minimum we deserved today. I'm pleased as well with the quality of our performance and our spirit. I'm a bit frustrated because I feel there was room to do more.
"We had early chances and of course very late chances, especially the chance of Gervinho at the edge of the box where we missed the target.
"But overall I hope the game will reinforce our belief, our confidence and reassure us about our potential in this league."
Source: PA
Source: PA