When the professional game showed itself to be profitable in the late 1920s, a number of amateur players joined the tour. One of the first to do so was William Tilden, perhaps the greatest player in the history of tennis. Before Tilden turned pro (1931), he won a total of seven United States singles championships and three Wimbledon championships.

The continued defection of amateur players into the professional ranks was one of the factors that led amateur tennis's world governing body, the International Lawn Tennis Federation (ILTF, founded 1913), to open its tournaments to both professionals and amateurs in 1968. For many years the major ILTF-sponsored tournaments, including Wimbledon and the U.S. National Championship, had been restricted to amateurs. With the advent of open tennis, however, the great professionals were allowed to compete for the major titles. Eventually, the Davis Cup also allowed professionals.