Koji Watanabe (渡邊康二, Watanabe Kōji, born 19 January 1942) is a Japanese former international tennis player. He won four career singles titles (1966-1969).
Watanabe played his first tournament at the Miami Invitational in 1961.[2] He won his first title on clay at Gruneweld, West Germany in August 1966 beating compatriot Ichizo Konishi in three sets.[2] In 1966 he claimed his second title again on clay at Ostend, Belgium defeating South African player Jackie Saul two sets to one.[2] His third title came in 1968 at the Lowther Hard Court Championships, Barnes, London where he beat New Zealand player Onny Parun two sets to one.[2] His fourth and final tile came in 1969 at the Athens International on clay where he defeated Australian player Geoff Masters three sets to one.[2] He reached the finals of three other tournaments Andhra Pradesh Championships on hard courts in (1966), the Worcestershire Championships, on grass in (1967) and finally Bad Neuenahar on clay in (1969).[2]
In Grand Slam tournaments he competed in the Australian Open two times, in 1965 and 1969.,[3][4] The French Open in 1964 and 1966 and at Wimbledon one time in 1969. He also served as coach for Japan's Davis Cup team (1971–1974) and as vice-chairman of the Japan Tennis Association.[4]
He played his last tournament at the Tokyo Indoor in 1971 losing to Ian Fletcher in the semifinals.[2]