Nelson pitched all or part of nine seasons in Major League Baseball between 1967 and 1976 with a record of 29 wins, 32 losses, and 5 saves.

He was traded along with Don Buford and Bruce Howard to the Baltimore Orioles for Luis Aparicio, Russ Snyder and John Matias on November 29, 1967.

After struggling with injuries in 1970 and 1971, Nelson bounced back in 1972 to finish fifth in the league in ERA (2.08) and also setting career bests with 11 wins and 120 strikeouts.

Nelson was dealt along with Richie Scheinblum to the Cincinnati Reds for Hal McRae and Wayne Simpson two months later on December 1, 1972.

He was released by the White Sox before ever pitching for them, and after a brief turn through the Oakland Athletics farm system, Nelson got one last chance with the Royals in 1976, appearing in 3 games in September to end his major league career.