National Champion 1954, 1956, 1960
National Doubles Champion 1949, 1950, 1951, 1953, 1954, 1958, 1959, 1961, 1962, 1965, 1966
U.S. Open Champion 1955, 1959

Diehl Mateer, with his unmatched eleven national titles, was the greatest doubles player the game had ever seen. With his classic Philadelphia backhand and indomitable determination, he was unstoppable on the left wall. He won his first doubles title as a senior at Haverford College with Hunter Lott, and went on to win titles with Cal McCracken, Dick Squires, John Hentz and Ralph Howe. He lost nine times in the finals, including twice with his son Gil (his boys Gil and Drew took five doubles titles in all, once together in 1986). On the singles court, Mateer was equally formidable. He took two intercollegiate titles, won six Harry Cowles, six Gold Racquets, five Atlantic City Invitationals, and was the only amateur to win the U.S. Open twice.