Beale, one of Deans's most dangerous attacking weapons when firing, was demoted to the bench for Australia's second straight defeat to New Zealand in Auckland last month after playing a dreadful match in the opener in Sydney a week earlier.
"He's in a better space. I don't think you'll see a performance like that from Kurtley again," Deans told reporters. "He's too good a player for a repeat of that.
"It was just one of those nights really. It goes from bad to worse and just compounds. It's in the past fortunately. I've seen a player that's very keen not to have a repeat."
Beale slots in at full-back, with Adam Ashley-Cooper shifting to outside centre to replace the dropped Rob Horne.
Deans said that 23-year-old Melbourne Rebel had been putting in the hard yards in training to rectify his mistakes.
"He's working hard on and off the field. He's doing his homework, making sure he's around the detail, which helps a lot in terms of positioning. You're less likely to get exposed," Deans said.
Queensland Reds speedster Dom Shipperley will make his debut after being named on the right wing, replacing Drew Mitchell, who was injured in his first Test back against the All Blacks at Eden Park after spending nearly a year on the sidelines.
"He's a young man that's brimming full of confidence and he's very excited," Deans said of the new starter. "He looked like he put on half a yard at training today."
The winger, though, played down expectations of a dazzling debut display.
"I just want to do my job. You can't go out and expect to set the world on fire in your first Test," Shipperley said.
"It's a pretty special feeling (to be selected). It's one of those things you never forget."
Back-rower Scott Higginbotham has been dropped to the bench in favour of 36-year-old Radike Samo, who takes the number eight position in an otherwise unchanged forward pack.
Powerful hooker Tatafu Polota Nau has been named on the bench after being withdrawn from the Eden Park test due to injury.
Australia, without a point and bottom of the standings after two rounds, must defeat the Springboks to keep their slim title hopes alive in the inaugural Rugby Championship, which sees Argentina debut in the southern hemisphere tournament.
Team: 15-Kurtley Beale, 14-Dom Shipperley, 13-Adam Ashley-Cooper, 12-Berrick Barnes, 11-Digby Ioane, 10-Quade Cooper, 9-Will Genia (captain), 8-Radike Samo, 7-Michael Hooper, 6-Dave Dennis, 5-Nathan Sharpe, 4-Sitaleki Timani, 3-Ben Alexander, 2-Stephen Moore, 1-Benn Robinson
Replacements: 16-Tatafu Polota Nau, 17-James Slipper, 18-Scott Higginbotham, 19-Liam Gill, 20-Nick Phipps, 21-Mike Harris, 22-Anthony Fainga'a