The Canford prospect took 3-28 as South Africa were dismissed for 230. England were ahead of the required rate at 137-2 when rain ended affairs in the 29th over.
Having already beaten Scotland, England are top of the four-team group and will remain so if they beat the West Indies in their final last match. Under Hampshire's Tom Prest, England were beaten finalists in the 2022 U19 CWC.