Proteas captain Temba Bavuma revealed on Monday that South Africa would make only one change for the third Test, with Coetzee in for the injured Anrich Nortje.
Off-spinner Simon Harmer has again held his spot as the home side's sole spinner, keeping out mainstay Keshav Maharaj based on the number of left-handers in Australia's team.
South Africa had the option to bring in Corbin Bosch or the more experienced Dane Paterson for Nortje, but preferred Coetzee's speed for his first Test in two years.
"I think he's probably the closest guy in terms of like-for-like for Anrich," Bavuma said of Coetzee.
"In terms of the role Anrich plays in our bowling attack as an enforcer, Gerald does that when he plays.
"We did consider the fact he hasn't played for a while, but he's been with the team getting his workloads in.
"He is a guy we believe has the ability to make a big play for the team."
South Africa can usurp Australia into the top spot on the ICC rankings with victory in Cape Town, adding that title to the Test Championship mace won last year.
Bavuma said he still ranked that victory in the final against Australia as more important than rankings, but there was still plenty driving the Proteas this week.
"There is a massive desire there, especially for the older guys," Bavuma said.
"In the last Test series in Australia, they bullied us in their backyard. They played unbelievable cricket
"There is that motivation for us to right those wrongs. And also to look after our home record.
"There is a lot to it. I don't feel I have to motivate anyone to ensure the result goes our way."
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