 Johnson made his professional debut in 1984.He won the WBA Inter-Continental middleweight title in 1989, and the USBA middleweight title in 1990, before losing a disputed split decision in 1991 against James Toney for the IBF and lineal middleweight titles, a fight in which he notably knocked Toney down in the second round.In 1992 he won his first world championship by winning the vacant WBA middleweight title in a close decision over Steve Collins.