S.A. Rumjahn won a total of 23 major Hong Kong titles, which were almost all on grass. He won five Men’s Singles at the Hong Kong National Grass Court Championships between 1927 and 1940, and thirteen Men’s Doubles titles (partnering his cousin, H.D. Rumjahn) between 1925 and 1940. In the 1940 singles final, the much older S.A. Rumjahn was given little chance against the leading player of the day, Tsui Yun Pui. His upset win prompted the local press to label it as one of the biggest upsets in the territory’s tennis history.