After Mourinho had suggested City were the beneficiaries of refereeing decisions his counterpart hit back about the amount of money the Blues had spent in January.
But, with Chelsea moving top of the Barclays Premier League table over the weekend as they easily saw off Newcastle 3-0 while City laboured to a goalless draw at Norwich, Mourinho turned the tables on Pellegrini's comments - hinting that the Chilean should know better given his background as a civil engineer.
"What I would like to say that Pellegrini was talking about the money we've spent," he said.
"I think he's a fantastic coach, and I respect that a lot, and on top of that, outside his football career, he's an engineer by academic formation.
"I don't think an engineer needs a calculator to do [Juan] Mata £37million and [Kevin] De Bruyne £18million, so that's £55million.
"[Nemanja] Matic is £21million and [Mohamed] Salah is £11million. That's £32million. 55 minus 32 is 23. So Chelsea, in this transfer window, generated £23million. It's easy to understand that this is working with financial fair play, fair financial fair play.
"There are no arguments against that. This is what we're doing. Others aren't doing the same. We are building a team for the next decade, if possible. They have a team to win now because they don't have a team for 10 years.
"They have a team for now, for the next three or four. So experience, potential, power, not worried about Financial Fair Play because, in the summer, they just spend... We don't need a calculator for this. It's easy. Plus 23.
"He has a fantastic team, fantastic players, is a good manager. Has lots of experience, so it's not a problem for him. 13 matches are 39 points, and that's an eternity in a league.
"He's been speaking about winning four competitions, so there's no reason to change the speech. But the only thing that is funny that he keeps saying he never responds to Mourinho, he never comments about Mourinho. He said that in Spain, too. So, he's changed."
Chelsea travel to struggling West Brom on Tuesday night looking to maintain their lead at the top but Mourinho knows any of the title contenders could falter when least expected to this campaign.
"Maybe the teams not in the top four will be very influential in the league," he said.
"Normally, people are pushed to say Chelsea against Arsenal, or Arsenal against City, or Liverpool against City. These are the matches that decide things. But maybe they aren't.
"In other leagues, it is like that. Madrid v Barcelona decides the title. Benfica v Porto decides the title. It's not the same situation here. The title is decided match after match.
"Every game is important. If we don't win tomorrow, it's not just about the title contenders to jump to the leadership again. It's also about Tottenham to win, Everton to win, and closing also the gap. At this moment, every point is important."