Clark Edward Graebner (born November 4, 1943) is a retired American professional tennis player.

[5] Graebner won his first important international tournament in December 1965 at the Victorian Championships at Melbourne's Kooyong Stadium.

Graebner won the Pennsylvania Lawn Tennis Championships at the Merion Cricket Club defeating Charlie Pasarell in the semifinal and Stan Smith in the final.

At the U.S. Championships at Forest Hills, New York he reached the quarterfinals where he was defeated by Stolle, who would win the title that year.

[7] Graebner won the Buffalo Indoor Tennis Championships[8] in February defeating Marty Riessen in a marathon final.

3 for 1967, which would be his highest world ranking, by the Martini and Rossi panel of tennis experts using a point system for tournament play.

Graebner then reached the semifinals in singles at the 1968 Wimbledon, defeating both Manuel Santana and Stolle, before losing a close match to Roche.

He won the 1968 U.S. Men's Clay Court Championships in Milwaukee defeating Charlie Pasarell in the semifinal and Stan Smith in the final.

At the inaugural US Open, he defeated Newcombe in the quarter-final, but lost the semifinal to Arthur Ashe, the eventual champion.

John McPhee's book, Levels of the Game, is about a semifinal match played between Graebner and Ashe at the 1968 US Open at Forest Hills.

Graebner won seven tournaments in the 1969 season, beginning with the Richmond WCT Indoor in February, defeating Thomaz Koch (winner over both Ashe and Richey in the event) in the final.

At Wimbledon in 1969, Graebner defeated Ilie Năstase and Andrés Gimeno before losing to Roche again in the quarterfinal, this time in a marathon five sets.

He won the U.S. Hard Court Championships in Sacramento in June, defeating Erik van Dillen in a close five-set final.

That same season, Graebner won the Southampton Invitational at Long Island on grass, defeating Bill Bowrey in the semifinal and Lutz in the final, both matches in three straight sets.

[7] He won the 1970 River Oaks International Tennis Tournament on clay in Houston, Texas, in April defeating Santana in the semifinal and Cliff Richey in a close five-set final.

In the Pennsylvania Lawn Tennis Championship at the Merion Cricket Club, he defeated Frank Froehling in a close semifinal and Dick Stockton in the final.

This was a rewarding victory for Graebner who had finished as runner-up at South Orange in 1964 (to Ashe), in 1966 (to Roche), in 1967 (to Riessen), in 1968 (to Pasarell), and in 1969 (to Smith).

[13] In the 1972 Rothmans International Tennis Tournament at the Royal Albert Hall in London, England, Graebner defeated Năstase in the semifinal, but lost the final to Richey.

[16] Graebner won the Long Island Indoor title in April defeating Roscoe Tanner in the final.