The midfielder was set to leave Bayern Munich on a free transfer in 2006.
And he admitted the lure of Mourinho convinced him to make the move.
Speaking about his decision to join Chelsea on Sky Sports' Transfer Talk podcast, Ballack said:
"One of the first were Man United to show interest, but they also hasn't had the best year. I remember 2006 they went out in the group stage [of the Champions League].
"Winning the league is one thing but for me it was always the dream to win the Champions League. And what team could I really attack this trophy with? It was not easy to decide because there are so many good clubs but Man United in those days were not as good as before, like Bayern Munich – 2000, 2001 and even 1999 they had their best years.
"I chose Chelsea and the package was really good. I felt really comfortable with it, and London for me was also a point, an argument to join a great city.
"When you're 29 and you've already got family, it's important that they feel comfortable. I talked to my family and we made the decision to go to London.
"I gave the sign quite early to my agent that I would prefer Chelsea from the beginning. If we could agree on the numbers and the circumstances, then that would be my preference."