He was Southern California men's champion at the age of 11.[10] Klein won the U.S. National Boys 15-under Championship (at age 13) and the respective age groups at age 16, 17, and 18.[9] At age 18, he also won the National Juniors title, and the National Men's Singles and Doubles Championships.[9] In 1955, he and Richard Bergmann won the U.S. Open Table Tennis Men's Doubles Championship.[7]
In 1956, he, 17 years old, and Leah Neuberger won the World Table Tennis Mixed Doubles Championship in Tokyo.[7][11] was a four-time US Open Table Tennis Singles Champion. In 1956 and 1961, he was the U.S. singles champion.[9][12] In both 1964 and 1965, he won the U.S. Open Table Tennis Men's Singles Championship, and he and Bernard Bukiet won the U.S. Open Table Tennis Men's Doubles Championship.[9][7][13]
In 1973, he was a member of the United States table tennis team that competed against China.[9]