The Italian insists his side must remain composed throughout the campaign and has pointed to Sergio Aguero's injury as to why City have not replicated their start from last season
City currently sit seventh in the Premier League, four points behind leaders Chelsea, after winning two and drawing three of their fixtures this term.
Mancini admits it is tougher to follow a title-winning campaign with a second league crown and the Italian insists his side must remain composed.
"We need to stay calm and work hard. We will win the title [but] I agree it is more difficult the second year," said Mancini.
At the same stage of the season last year, City had scored 17 goals in their first five league games but Mancini has pointed to Sergio Aguero's knee injury as the reason why his side have struggled to replicate their barnstorming start last term.
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]."