Former Chelsea and Manchester United boss Mourinho was appointed after the sacking of Mauricio Pochettino on Tuesday and he can expect a frosty reception from his opposite number when he makes his Tottenham bow at West Ham’s London Stadium.
The London derby will mark the latest chapter in the acrimonious relationship between Pellegrini and Mourinho.
The long-running feud began when Mourinho succeeded Pellegrini as Real Madrid boss in 2010 after the Chilean guided Los Blancos to 96 points in La Liga, the highest points total they had ever achieved.
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Asked what he would do if he were to be fired by Real Madrid as Pellegrini had been, Mourinho who referred to Pellegrini as ‘Mr Pellegrino’, said: “If they get rid of me, I won’t be going to coach Malaga. I will go to a big club in the Premier League or Serie A.”
After winning every domestic title available for a manager in the Spanish top division within two years and surpassing Pellegrini’s record La Liga points total, Mourinho returned to Chelsea after leaving Real Madrid by mutual agreement in May 2013.
The feud was re-ignited in the 2013/14 season when Mourinho and Pellegrini managed Chelsea and Manchester City, respectively. “I don’t know him. He worked in Spain, I worked in another club. We played Real Madrid against Malaga, nothing more. I don’t have any complaint about him,” said Pellegrini.
But the relationship turned sour when Fernando Torres capitalised on a last-minute mix-up in Manchester City's defence to give Chelsea victory at Stamford Bridge in October 2013.
Pellegrini refused to shake Mourinho’s hand after the Portuguese manager celebrated wildly by jumping into the crowd.
After the game he said: “I did not expect anything different from him. It is normal. It is a different way to celebrate from me.
“No, I didn’t shake hands because I didn’t want to. I repeat, I didn’t want to shake hands. I don’t want to say more.”
The war of words continued when Mourinho claimed Chelsea were ‘little horses’ in the title race in February 2014.
“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, 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.”
Never one to shy away, Mourinho retorted: “Academically he is an engineer and he does not need a calculator to work it out. Mata was sold for £37m, De Bruyne £18m. That is £55m. We brought in Matic for £21m and Salah for £11m – that is £32m. So £55m less £32m is £23m. So for Chelsea in this window it is £23m – he does not need a calculator for this.”
After Chelsea won the title by eight points in 2015, Pellegrini said: “When he wins, Mourinho wants to take credit for everything. I never do that.
“I differ from him on all fronts. I have no interest in analysing him as a person.”
He then attacked Mourinho in his book, branding his Chelsea side ‘selfish’.
“It used to be said that Mourinho’s Chelsea were boring,” Pellegrini wrote. “I don't think that’s true at all.
“Chelsea are selfish not boring. It’s a team that puts a lot of emphasis on what they do without the ball.
“And in my opinion that concept of football doesn't respect the spectacle.”
The dust has settled since the pair traded verbal barbs and Pellegrini has played down the long-standing rivalry ahead of their re-union in front of the BT Sport cameras on Saturday.
Speaking at the pre-match press conference, the 66-year-old said: “He is not my friend but he is not my enemy either. Maybe I think a different way but he is not my enemy. Everyone has their options to play football the way they want and what they want to say. We have different ways of thinking about it all.
“The table is very tight, we must try to recover our performance as individuals and as a team and I hope this will be a good game to return to winning ways.”
Pellegrini has poured cold water on his rift with Mourinho but will tensions boil over and old grievances come to the fore in the heat of battle at the London Stadium on Saturday afternoon?