The Ghana international was reduced to a bit-part player under Roberto Di Matteo after a serious knee injury, but was offered a lifeline at Real Madrid by then-manager Mourinho in a second-long loan deal.
Essien, who hailed Mourinho's talents following his unveiling on Monday, played at the back and in midfield at Santiago Bernabeu and is ready for whatever the Portuguese needs.
"I don’t mind playing anywhere for Chelsea under Jose Mourinho,” Essien told Goal. "I am always positive and I will work hard and make myself always available for him.
"Where I play doesn’t matter just put me on the pitch and I will do the business for the club. I don’t have much to prove. I have done it all, so I just go out there, work hard and win games."
The 30-year-old was signed from Lyon for 29 million euros by Mourinho in 2005, a then-club record fee, going on to make nearly 100 appearances in all competitions - winning two Premier League titles along the way - before the manager left the club in September 2007.