The 55-year-old Chilean was installed on Tuesday as Real's 12th coach in 11 years and will be charged with making the spectacular sporting project promised by new president Florentino Perez into reality on the pitch.
At Villarreal, where Pellegrini's sole piece of silverware in five seasons was an Intertoto Cup in 2004, he was closer to an English-style manager, with a good deal of influence over the buying and selling of players.
Villarreal's board backed him over Juan Roman Riquelme when the pair fell out in 2007 and the Argentina midfielder was soon on his way to Boca Juniors.
The list of high-profile Real bosses he will be dealing with is long and the pressure to return the nine-times European champions to winning ways immense.
As well as Perez, who went through six coaches in his first term at the helm in 2000 to 2006, Pellegrini will answer to former coach and new director general Jorge Valdano, who pushed hard for his appointment.
Next come former player Miguel Pardeza, who has replaced Predrag Mijatovic as sporting director, and Zinedine Zidane, one of the "galacticos" Perez brought in at huge expense during his first term, will be a special adviser to the president.
Perez and Valdano have repeatedly emphasised that Pellegrini will have full authority over the squad and no players will be bought without his approval.
But past experience shows the construction magnate does not always back his coaches in transfer decisions.
Jose Antonio Camacho, who helped save Osasuna from relegation this season, quit Real in 2004 complaining the decision to sign striker Michael Owen rather than the midfielder he wanted was just one sign of his limited clout.
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Some in the Spanish sports press have said Pellegrini's contract of only two years suggests he is an interim solution rather than a long-term one and will eventually be replaced by a bigger-name coach.
Asked by Reuters at a news conference on Tuesday how much decision-making power he would have at Real compared with Villarreal, Pellegrini said: "Exactly the same."
He added that the hiring and firing of so many coaches in recent years did not worry him and he was confident of success.
"Big clubs are always required to win every Sunday and it's difficult to keep a project going if that's not happening," he said. "But usually those that have a long-term project and know how to keep it going are those that get the best results."
Perhaps Pellegrini's most demanding, and least patient, master will be the fans in the Bernebeu.
Having just watched their arch rivals Barcelona win the treble, they are ravenous for quick success.
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