The Nigeria international was signed by Mourinho in his first spell in charge during which the Portuguese boss won five trophies in three seasons.
Mikel said Mourinho had returned to the club this summer with the sort of swagger which convinces players they can do better.
"This game is all about winning and the manager that brought this transformation of winning to this club is back now," Mikel told Chelsea TV.
"He still has the same idea of how he wants us to approach every game with a win, win mentality.
"I came to this club at 18 and he made me to think 'win, win, win'. Whenever you see him, you see motivation.
"He walks around the place full of energy, full of confidence, and really, he is not doing it for himself but for you to see how he goes about his business.
"He wants you to emulate that into yourself and start behaving in a similar way.
"This is because confidence can lead you to so many places that you never thought you could go and it is just brilliant to work with him again.
"And now that he is back, we hope that we can continue winning the trophies that we won since he left."
Summer signing Willian believes he is feeling the benefit of the Mourinho effect.
The 25-year-old moved from Shakhtar Donetsk late in the August transfer window and the switch has seen him regain a place in the Brazil squad for friendlies against Honduras and Chile.
"I was even a little surprised by the news," the midfielder, who last appearance for the national side was in 2011 prior to current boss Luiz Felipe Scolari taking over, told Brazilian newspaper Lance.
"I am happy with myself, as I think I am improving every match. I'm feeling physically better and slowly becoming more confident.
"I am sure I'll grow even more, improve with every game. What is important is that I am happy and that I am earning my place.
"I am delighted to receive another chance. I've been called once and it is great to have another opportunity.
"I hope to grab this chance with all your strength, do a good job and realise my dream to play in the World Cup."