The 33-year-old centre-back, who endured an indifferent season at Stamford Bridge during the 2012-13 campaign, has been ever present in defence that has seen the West London outfit boast the least number of conceded goals so far this term.
Mourinho told Sky Sports News: "I was not expecting him to be the best centre-half in England. Not after the season he had last year. I was not expecting it.
"I would like to see him playing this way until the end of the season."
Mourinho's men travel to Eastlands for a clash with Manchester City tonight.