The hosts are attempting to respond after suffering a 214-run defeat in Durban, but their progress has been hampered by persistent rain, with only 43 overs bowled across the first two days.
Australia paceman Scott Boland has exploited the conditions effectively, claiming four wickets for 31 runs to leave South Africa struggling at 97/5. His victims included Aiden Markram, dismissed for 11, and David Bedingham, who edged behind to Alex Carey.
Petersen believes captain Temba Bavuma has demonstrated the composure required, urging the middle and lower order to follow suit and build a competitive total.
"I think it's going to be tough because, obviously, every time you come here, there's moisture in the surface. It's almost like the grass stands up. And that's what the bowlers want, someone like Scott Boland, who can be compared to Vernon Philander," Petersen told IOL.
"They want something where they can pitch the ball, get the seam to scramble a bit and go both ways. So I think it's going to be tough.
"What I've seen in recent seasons is that the guys are actually reaching for it, whereas you have to go in and play the ball late. But it's difficult.
"It takes a while for you to really get used to the tempo and all of that, and when you feel like you can do so early on, it's going to be a real struggle.
"If you look at the two teams, Australia and South Africa, South Africa will have two choices… Now the question is, how are you going to play? Are you going to try and make something happen? It's hard to say."
South Africa produced a dominant performance to beat Australia by an innings and 31 runs in the second Test at St George's Park in Gqeberha on Thursday, levelling the series at 1-1.
South Africa produced a commanding performance to defeat Australia by an innings and 31 runs in the second Test at St George's Park in Gqeberha, with captain Temba Bavuma leading the way with a magnificent 179.
Marco Jansen took a five-wicket haul as the Proteas skittled Australia out for just 99, before the tourists found themselves in trouble following-on at 156-4, still trailing by 170 runs.
Springbok legend Victor Matfield believes the world champions will play with more of an attacking edge on their tour of Europe after leaning heavily on their traditional physical strengths during Rugby's Greatest Rivalry series.
