There was a feeling City lacked the mental toughness of their rivals last season as they meekly surrendered the Barclays Premier League title they won in 2012.
Pellegrini does not share that view of the squad he inherited in the summer and is bullish of his side's chances ahead of Sunday's eagerly-anticipated Manchester derby at the Etihad Stadium.
The Chilean said: "I don't know what happened in the past but I know that our mentality in this moment is very strong, so strong or more strong than Manchester United."
City finished 11 points behind champions United last season.
The significance of this weekend's derby in local terms and in the wider context of the title race is not lost on Pellegrini.
The 60-year-old said: "I don't need to be here to know how important the derby is, but working here and living here I know it is a special game.
"It is a match of six points. It is very important to win (against) one of the most important teams.
"It is more important to win than not to lose."
Pellegrini may be new to the Manchester derby but he is no stranger to big rivalries having previously managed at Real Madrid and River Plate.
Pellegrini, who has been living in a Manchester hotel since his appointment, said: "Real Madrid-Barcelona is a very important derby and River-Boca (Juniors) also, but when you live in the city every day you feel how important this derby is for the city of Manchester, for both sides.
"The last week all the people are talking about the derby, I know it is a very important derby and the most important match for this club."
Sunday's clash will be the first Manchester derby since 1986 in which Ferguson has not been in the United dugout.
Pellegrini believes former Everton boss Moyes was a good choice of successor for the long-serving Ferguson but has reminded him of the pressures he faces.
He said: "It was no surprise because he has had a very good career here in England.
"Maybe he didn't win a title because it is very difficult to win a title if you are not at four or five teams but he has all the merits to be the manager of Manchester United.
"It is impossible not to be under a lot of pressure, not in replacing Alex Ferguson but in managing Manchester United, or big teams.
"You are always under big pressure but that is a good way to work because you know what you have to do."