Scott Boland's form continued in a rain-soaked second Test continued overnight, as the Gulidjan quick carried on causing troubles for South Africa's batting order with Australia pushing for a series win in Gqeberha.
A wet morning halted play until well into the afternoon at St George's Park but a relentless line and length, and a screamer from Matt Renshaw in the slips, saw Boland add to his two day one wickets and go to stumps with figures of 4-31.
The Proteas will cling to faint hopes of forcing the contest back in their favour at 5-97 ahead of the third day of play.
On return to the Australian XI, Boland immediately vindicated selectors' decision to pick him over veteran spinner Nathan Lyon and opt for the four-pronged pace attack when he removed Aiden Markram and David Bedingham in consecutive balls either side of Sunday's earlier rain delays.
Despite hours without rain, a soaked outfield prolonged the wait until mid-afternoon on Monday.
Australia didn't arrive at the ground until after 2pm and were without an ill Josh Hazlewood in the bowling rotation for the day.
Somehow, a full session's worth of overs were completed late in the piece. A collective 43 overs have been completed in the match following 12.2 on day one.
In just the second full over of the day Boland had debutante Marques Ackerman nicking through to Alex Carey's gloves, departing for a patient 6 from 38 balls in his start to Test cricket.
A short time later, Mitchell Starc induced a stroke with a wider one to dismiss Matthew Breetzke (4 from 17 balls).
Proteas skipper Temba Bavuma (still unbeaten) and keeper-batter Ryan Rickelton steadied to put on a 50-run partnership.
Rickelton survived when a catching chance was dropped, but Boland returned to move Australia into the lower middle order in the final overs of the afternoon.
Carey didn't move for an outside edge, leaving things up to Renshaw at first slip to create something special. The 194cm batter dug down towards his right ankle to snap up the chance and give Boland 4-30 inside 13 overs.
On a particularly green surface, helped by moisture from the weather, Boland has been the pick of the visitors' bowlers and the only one to create significant movement with the ball.
South Africa have spearhead quick Kagiso Rabada back in their line up when Australia enters the crease to partner with Marco Jansen and Anrich Nortje, who did serious damage on his return to Test cricket in Durban.
Playing his 20th Test, Boland is edging towards 90 wickets with an average just marginally over 18.
A third five wicket haul is within reach when play resumes.
