2 June 1935
Cricket in South Africa was established by the British, and the first tour by a side from England took place in 1888-89. Here South Africa played its first Test match (against touring England at Port Elizabeth), becoming the third Test nation. South Africa's first win on English soil came in the Second Test at Lord's in 1935, taking the 5 test series 1 - 0 with a victory by 157 runs thanks to Bruce Mitchell's 164 and Jock Cameron's quickfire 90. The match was one of the first to include a new LBW law that said batsmen could be out to a ball pitching outside the line of the stumps.  
References

Wallis, F. (2000). Nuusdagboek: feite en fratse oor 1000 jaar, Kaapstad: Human & Rousseau