Chelsea beat Pellegrini's team 1-0 at the Etihad Stadium on Monday night to draw level with second-placed City on points, two behind leaders Arsenal.
However, Mourinho insisted after the match that City and Arsenal remained favourites for the title, describing his side as a "little horse that needs milk and needs to learn how to jump".
However, for the first time Pellegrini has opted to return fire, implying that Chelsea's significant outlay in the transfer market renders Mourinho's remarks debatable.
"Maybe it is a small horse if the manager thinks like that," said Pellegrini. "It can be a little horse, but very rich.
"This is the team that has spent most money in the last 10 years, it is the team that spent most money this year, and the team that spent the most money in the transfer window. So, little, but rich."
Pellegrini expects close race
And Pellegrini went on to say that, having done the double over City, Chelsea are clearly in contention for the title, despite Mourinho's remarks.
"He has shown in the last two games he has a strong team with some great players," said the City boss.
"I think he is favourite. He thinks, if he wins, he will have the merits but, if he loses, he does not have responsibility.
"It is the way he acts. Everyone acts the way he thinks is better for the team.
"I think it will be very close with Chelsea and Arsenal.
"Arsenal are the favourites because they have two points' lead in the table.
"Of the 24 games we have played, Arsenal have been top of the table for 16 or 17. They have an important advantage.
"I am sure the three will fight to the end for the title."
Boss wary of Norwich
City will attempt to get their challenge back on track at Norwich on Saturday and Pellegrini does not expect a repeat of the 7-0 thrashing his side handed the Canaries in the reverse fixture.
"It's a very difficult game," he said. "It is very important the way the team reacts after the defeat at home.
"We play against a good team in Norwich, a team that tries to play, so we hope that we can win again.
"It will be absolutely different. They will want revenge for what happened here.
"They have a good team that play good football. It is very important for us to continue playing the same way we are doing away, because we won all of the last four games."