Agassi confesses they were a terrible match, but blames himself for the ill-fated union - which ended in divorce in 1999 - claiming he clung to Shields in a desperate bid to find happiness during an emotional meltdown.
He explains, "(I was) 27 years old, ranked 141 in the world and in a marriage that I shouldn't be (sic) in... I didn't want to be playing tennis either so my life was filled with things I didn't want, things I didn't choose. Part of it was an inability to find a place for anything really."
Agassi married fellow tennis champion Steffi Graf in October 2001. They share an eight-year-old son, Jaden Gil, and a six-year-old daughter, Jaz Elle.
The revelations feature in Agassi's new memoir Open, in which he also admits to taking crystal methamphetamines and deliberately throwing tennis matches.