Damiani began his professional career on a tear, with 27 consecutive victories over limited opposition. He defeated Tyrell Biggs in a rematch of their Olympic meeting, stopping him on a cut, and then won the newly created WBO Heavyweight title with a 3rd-round KO victory over Johnny DuPlooy on 6 May 1989. Damiani hit a brick wall when he took on 1988 Olympic Gold Medalist Ray Mercer in 1991 in Atlantic City, New Jersey. Damiani was ahead on points but went down after a Mercer left uppercut broke his nose, and he was counted out by the referee in the 9th round.