He said: "I was with him for three years. We are different, but the mentality that we have about our job is the same. We think 24 hours per day, 100 per cent every day about our job.
"At the beginning he was criticised and, at the moment, he has two titles in his pocket."
The pair, who will go head-to-head at the Riverside Stadium on March 19, still speak on a regular basis, and Karanka admits that the advice he receives from one of the game's highest-profile managers is invaluable.
He said: "Always, especially in this situation, when you have help from your friends, it's good."