Two specialists who supervised trades on the floor of the New York Stock Exchange pleaded guilty Friday to securities fraud in what a prosecutor called a “groundbreaking” development in a new area of prosecution.

Joseph Bongiorno, 51, of Brooklyn, and Patrick McGagh Jr., 40, of Little Silver, N.J., entered the pleas in U.S. District Court in Manhattan, admitting that they illegally put their companies’ orders ahead of orders from the public.