The Portuguese coach officially launched a new era at Valdebebas, where the available players completed medical examinations before taking part in their first training session of the European summer.
Only eight first-team players were present, with Andriy Lunin, Trent Alexander-Arnold, Marco Asensio, Dean Huijsen, Alvaro Carreras, Eduardo Camavinga, Franco Mastantuono and Gonzalo Garcia all taking part.
Many of Real Madrid's senior stars are still on holiday after their World Cup commitments, while others remain involved in the tournament, with the semi-finals set to begin on Tuesday night.
With numbers limited, Mourinho promoted 16 academy players to train alongside the first team as they begin preparations for the new season.
Among those included was Cesar Palacios, despite reports suggesting he could leave the club this summer to continue his development elsewhere. Highly-rated defender Joan Martinez also featured after being tipped to make his senior debut during the upcoming campaign.
Cestero, who has already played 113 minutes for the first team, was also involved, along with goalkeeper Fran Gonzalez and youngsters Mestre, Valde, Lamini Fati, Lacosta and Pol Fortuny.
Several players from Real Madrid C were also given an opportunity, including Cherif Fofana, Roberto Martin and Jacobo Ortega, who all helped the club win the UEFA Youth League last season. Lezcano, Melvin, Alexis Ciria and Gabri Valero completed the group after stepping up from the Juvenil A side.
A number of promising youngsters were absent from the opening session. Thiago Pitarch, Yanez, Diego Aguado, Jesus Fortea, Javi Navarro and Mario Rivas are expected to report later after helping Spain win the UEFA European Under-19 Championship earlier this summer.