Paceman Kagiso Rabada rocked Australia with five wickets in 18 deliveries as the tourists were rolled for 243 after electing to bat first.
It was Rabada's eighth five-wicket haul in only his 28th Test match and his second against Australia. He was well backed up by Vernon Philander and Lungi Ngidi as Australia collapsed from 98-0 to 243 all out.
Rabada was involved in a fiery send off after trapping Steve Smith in front of his stumps.
Coming in as nightwatchman, Rabada will resume on 17 after supporting Elgar (11 not out) as South Africa reached 1-39.
South Africa 39 for 1 (Rabada 17*, Elgar 11*) trail Australia 243 (Warner 63, Rabada 5-96, Ngidi 3-51) by 204 runs.
Matches Tagged in ClipDex2018 RSA v AUS 2nd Test
Series Tagged in ClipDex2018 RSA v AUS Test serie ...
Players Tagged in ClipDexCummins, Patrick J Rabada, Kagiso Bancroft, Cameron T Philander, Vernon D Ngidi, Lungisani Khawaja, Usman Tariq Markram, Aiden Starc, Mitchell A Warner, David
Grounds Tagged in ClipDexSt George's Park
Categories Tagged in ClipDexTest Matches