Stanley was selected by the Los Angeles Dodgers in the ninth round of the June 1973 MLB draft, but did not sign with the team, choosing to start college. During this era, another draft was held in the winter; Stanley was selected by the Boston Red Sox in the first round of the January 1974 secondary draft, and he signed with the team. He began his professional career with the Elmira Pioneers in 1974, spent 1975 with the Winter Haven Red Sox, and advanced to the Bristol Red Sox at the Double-A level in 1976.