Spinners could have a deciding say on the final two days of the Newlands Test which will determine both who wins the series between South Africa and Australia and who holds the No.1 ranking.

The pitch, which has been flat and conducive for run-scoring, has already started to take turn, and the increasing number of puffs of dust suggest there is more on the way. Nathan Lyon has already taken one second-innings wicket - the crucial one of South Africa's captain Temba Bavuma - and with Mitchell Starc creating footmarks for Lyon to work with, the rest of the line-up are well aware of the threat he can pose.

Then, it will be over to South Africa's offspinner, Simon Harmer, who took 4 for 104 in the first innings and suspects he will have a huge role to play in the final act.

"Spin is probably going to come into it a lot more than it has in the first two-and-a-half days," Harmer said at the post-day press conference. "It was quite evident to see tonight how the ball was turning out of the footmarks. I don't know if the middle of the strip is going to start going up and down for the seamers, but the way that I see it, spin has a massive role to play in the rest of the Test."

Even with that expectation in mind, and Josh Inglis' suggestion that Australia "don't want them (South Africa) getting too many more than maybe 200," Harmer would not be drawn into predicting what he thinks will be a defensible total, with South Africa currently only 40 runs in the lead.

"It's a long way off," Harmer said. "It's cliched and simplistic, but the most important part of this game for us is the first hour tomorrow morning. We can't get too caught up in what we want and what would be nice and what is defendable, because whatever that looks like is not achievable if that first hour doesn't go well. It's just making sure that we don't get too carried away and look too far ahead. We try to keep it as simple as possible and just make sure that if we have a good hour tomorrow morning, it puts us in a much stronger position than trying to get 200 and getting sidetracked."

The lowest target successfully defended at Newlands is 208, when South Africa's seamer Vernon Philander bowled India out for 135 in January 2018. Conditions are vastly different for this match, which is the first Test staged in October at the venue. The first half of the match was played on what Harmer called a "quite placid" surface, on which South Africa threw away a promising start after a 158-run opening stand to lose 10 wickets for 171. Australia scored exactly 100 runs more than South Africa's 329 and they were satisfied with the way they managed to limit them after Australia were 370 for 4 halfway through the third morning.

"We understood that we couldn't let them get past the 100-run lead because then it can snowball very quickly," Harmer said. "And we knew that the only way that we were going to stop that is to take wickets. Yesterday the wicket was quite placid. We were just trying to figure out what we didn't do right yesterday, and understanding that with (inexperienced) Cooper Connolly coming in next and then the bowlers, there was an opportunity. Wickets have fallen in clusters, so there has to be that belief that once you open the door, you need to seize that moment."

That could also be a caution for South Africa. There were five ducks in their first innings and they lost four wickets in the space of six balls to Mitchell Starc with the second new ball. Though they bat deep, they understand that forming solid partnerships are the only way they will be able to stay alive in the series and then they will still need to bowl well if they hope to push for a win.

On the second front, Harmer is confident they can, but they will need the runs to work with to make it a reality. The surface, he believes, will play ball. "There's going to be a lot more on offer from the wicket's perspective," he said. "And there's a lot more on the line in terms of the result. The series is at 1-1. It's going to boil down to getting the ball in the right area the most amount of times and trying to keep it as simple as possible. We have to understand the occasion, enjoy it, enjoy the pressure and hopefully do something spectacular."