On a second straight day ruined by rain in Gqeberha, Boland finished with figures of 4-31 at St George's Park with the Proteas fighting to stay in the series after being sent in.
Matt Renshaw briefly stole the show late with a superb reflex catch at first slip, removing Ryan Rickelton and ending a long resistance with Temba Bavuma.
But it was Boland who was again the main man, after only learning on Sunday morning he would come into the side for Nathan Lyon.
Remarkably, the Victorian's record in his past 10 Tests is now greater than his first 10, taking 51 wickets at 16.52 over the past three years.
That is not insignificant, given the right-armer debuted with 6-7 at the MCG in the 2020-21 Ashes and had one of the greatest starts to a career in history.
He is also the oldest Australian seamer since Ray Lindwall in 1960, but there is no end in sight.
"I know I'm 37 and the oldest fast bowler to play for a while. But I still feel like I'm going really well," Boland said.
"My body's in a good spot so I feel like I can do it for as long as I can.
"I think that's the beauty of only playing one format. I know what my games are going to be. I can build up towards that.
"I don't have to worry too much about bowling yorkers or slow balls or things that put your action a bit out of whack."
After taking two wickets during a brief opening-day burst, Boland then struck in his second over of day two when he had a driving Marques Ackerman caught behind.
He then claimed Rickelton's wicket for 31 late in the day, when Renshaw stuck out his right hand at first slip and caught the ball just above the turf.
Boland has managed to come into this game hot, despite a one-day match for Victoria last month and tour game marking his only cricket since March.
He continues to take the approach that he must prepare to play every match and naturally wants to, but more often than not finds himself left out behind the big four.
Even so, his Test record of 86 wickets at 18.08 is now back in the top-10 averages of all time.
"I just want to be ready for whenever I'm needed. Obviously I want to play every Test but I know that's not 100 per cent realistic," Boland said.
"So I just want to be ready for whenever I get my opportunity and then try and impact the game straight away.
"We've got so many tests over the next 12 months that I knew I was going to play a part somewhere."
Boland's late blow on Rickelton was crucial given he and Bavuma (41no) had steadied the ship from 4-40, when Mitchell Starc had Matthew Breetzke caught behind.
Bavuma played a couple of sweet square drives off Starc and Boland, before stopping traffic when he hooked Pat Cummins for six and the ball bounced on to the road.
Australia were without Josh Hazlewood on day two, who remained off the field with illness.
The tourists are hopeful he will be back on the field on Tuesday, but he may need to go at least a session without bowling after spending time off.
The 30.2 overs of cricket came after heavy overnight showers wreaked havoc, with the rain stopped by 10.30am, but a wet outfield delaying play for a further five hours.
A win at St George's Park would wrap up the three-Test series for Australia after the 214-run victory in Durban last week, and make them the first visiting team to triumph in South Africa since England in 2019-20.
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