Winslow took 1907-1925 to tennis tournaments. In 1909 he won the championship of Transvaal, 1910 at the Natal Championships. In 1912 he joined tournaments in Europe, including at the Queen 's Club Championships, at. In the hard-court world championships in Paris, he reached this year in the doubles side of Harold Kitson the final. His greatest achievement was the victory in singles and doubles at the Olympic Games in Stockholm in 1912.
In 1914, he won the championship of South Africa in Johannesburg.
In his only appearance at the 1920 Wimbledon Championships he reached the second round. At the 1920 Summer Olympics in Antwerp, he could again win the bronze medal in singles.