City are in seventh place in the table and have not won in their last four games in all competitions, conceding 14 goals in seven games.
The Italian said: "I agree that it is more difficult the second year but we [will] win, we [will] win the title.
"I think this year all these teams are better teams and probably every game will be more difficult than last year."
Mancini pointed out that in the five Premier League matches his side have only let in two more than at the same stage last season, and blamed the pre-season disruption.
He added: "It's difficult because we didn't have 14 players in pre-season and had new players on the last day of the transfer market and they need time.
"Another reason we didn't work well in pre-season is because we didn't have all the defenders, but we have all these problems and conceded only two goals more than last year.
"We had the best defensive record for the last two seasons, but football is like this - sometimes you don't concede a goal for 10 games and then concede two or three goals. We need to work hard and have more concentration.
"Maybe we score less than last year after five games but we have had [injury] problems with Sergio [Aguero]."