The Ghanian made the move to Stamford Bridge for a reported £21.7m, replacing the departed Filipe Luis who has joined Atletico Madrid.
The club announced the signing moments after yesterday’s 3-0 hammered from Manchester City.
Mourinho spoke after the defeat: “It is important because he is a left-back. He can compete with Azpilicueta.”
“At the same time Azpilicueta can compete with Ivanovic for the right-back position, so he replaces Filipe Luis in the balance of the squad.”
Baba Rahman also spoke about the deal: “I am very happy to sign for Chelsea, one of the biggest clubs in the world.”
“I can’t wait to train with my new team-mates and am very much looking forward to working with them and Mr.Mourinho.”