Mancini: We will win the league
City are in seventh place in the table and have not won in their last four games in all competitions.
Mancini has blamed the disrupted pre-season, with many players returning to the club late due to international commitments, for the slow start.
The Italian admitted winning the second title is harder than the first, but insisted his side would pull off the feat.
Mancini 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."
City have had the best defensive record in the top flight for the past two seasons but this season so far they have looked fragile at the back, conceding 14 goals in seven competitive matches so far and without a single clean sheet.
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]."
Argentina striker Aguero returned to the starting line-up in the 1-1 draw with Arsenal last weekend, and French midfielder Samir Nasri will be back after injury for the match at Fulham on Saturday where City need to shake off the embarrassment of a 4-2 home defeat to Aston Villa in the Capital One Cup in midweek.
Mancini appeared to be fuming immediately after that match, but today insisted he had kept his cool.
"I wasn't angry, I was unhappy about the result and the performance," he said. "But we can't change the result and Aston Villa deserved to win, so we can only keep calm and keep going.
"There are some moments where maybe we don't play well and the other team play better than you and you are unlucky and that was one of these moments. We need only to stay calm and work hard.
"Maybe it is a good thing we went out of this cup so we have more time in October to work. We are upset but it could be good."
City came second-best to Arsenal in terms of possession even if the scores were equal, but Mancini said he was generally happy with how his team had kept the ball this season, and with their results away from home.
"I think the games we play at home against Southampton and QPR maybe we didn't play very well like last year, but we played a good game, scored three goals [in each match]. Maybe we conceded more goals than before but the ball possession was good."
City's only fresh injury is to midfielder Jack Rodwell, who will miss out against Fulham after injuring his groin in the warm-up before the Villa game.