The Etihad Stadium side maintained their five point lead at the top of the league after beating Alan Pardew's side 3-1 but the Italian feels that his team will suffer defeat
Mario Balotelli, Micah Richards and Sergio Aguero all got on the scoresheet before a late Dan Gosling strike for the visitors rounded off the clash, as Mancini's men moved eight points clear at the top of the table ahead of Manchester United's visit to Swansea City.
The victory was City's 11th in 12 Premier League games but Mancini is "sure" that his side will eventually slip up during the campaign, despite being impressed with their performance in what he believed was a tough fixture.
"Today was a really difficult match because Newcastle is a strong team, they have played very well and we knew this," he said. "After the international break is always difficult.
"Before the game I told the guys that it was going to be difficult - and if we want to win this game then we should play very well today.
"We played very well, we had a lot of possession, we scored three goals, we had other chances but in some moments we were also lucky.
"I hope that we can continue like this but in the 26 games that we have there will be a time that we will lose a game, I'm sure. But I'm happy for the players and I think we're playing very well because we have good players.
"The team has improved a lot, as players, as a team. I think we are a very strong team now but we should think that the season is long and probably there will be a difficult moment. For this reason it's important now if you can score goals and you can win. It's important."
Balotelli opened the scoring with an audaciously taken penalty on the 41st minute following a handball from Ryan Taylor and Mancini was full of praise for the 21-year-old, whom he described as a "great" player.
"With penalties Mario is fabulous. It's impossible for him to miss one penalty, I don't know why. He shoots very well.
"Mario is a very important player, he's a great player like all the players at Man City. He's becoming better and better and training well.
"Mario's doing all the work, I'm just helping him to not waste his talent become the player that he can become. The rest is up to him. It's possible that he will play in Naples."
Mancini opted to start with the talismanic David Silva on the bench at the Etihad Stadium and the Italian explained that the Spain international was in need of rest following Spain's 2-2 draw against Costa Rica in midweek.
"David [Silva], if he could, would play all the games but it's impossible like the other players," he said. "Sometimes he needs to rest. He arrived on Thursday from Costa Rica and he was tired for this reason."