The top-4 finishers in the 60-man field are given entry into the 133rd Open Championship at Royal Troon in July.
Tjaart van der Walt sits just one of the pace with 18 holes to play with Grant Muller in fourth place after 3-under 69.
Six other players are tied for fifth at 2 under including Richard Sterne.
Kingston and Oosthuizen both had strong days at the Atlantic Beach course that is usually known for heavy winds. Kingston enjoyed eight birdies and two bogeys while Oosthuizen, just 21-years-old, had seven birdies against a lone bogey.
The final 18 holes will be played Friday.