The world champions were made to fight all the way for their 55-53 win over the Proteas after Alexander benched skipper Caitlin Bassett, Steph Wood and midcourter Kelsey Browne who all starred in the win over New Zealand on Friday

But Alexander said the reasons for the changes were purely tactical and that the form of Caitlin Thwaites, who scored 30 goals from 30 attempts and Gretal Tippett (23/23) vindicated her decision.

"We are playing different opponents and not because we under-estimated South Africa at all," Alexander said.

"We felt the team matched up well on them and that shows we respect them."

The result means Australia are now one win away from a 12th World Cup triumph but Alexander acknowledged the performance was far from perfect despite the determination shown by her players.

"It was a bit nervy, but the great thing is that are putting in practice a lot of the things we have worked on over the last three weeks," she said.

"We are scoring when we have to score and getting turnovers when we need them.

"That's what needs to happen to win these types of games.".

The Proteas who are coached by former Diamonds mentor Norma Plummer were looking to reach the final for the first time, and at one stage in the fourth quarter had reduced the deficit to a single goal having trailed 31-23 at halftime.

But Plummer was left to rue some poor finishing by shooters Lenize Potgieter and Maryka Holtzhausen, who missed four attempts between them.

"It wasn't a walk in the park after all, was it," said Plummer, who refused to be drawn on whether the Diamonds selection was an insult to her team.

"(They were) very lucky to get out of it because we had the opportunity in that last bit being one goal down," she said.

"But not maintaining pressure at that time cost us. We worked that hard, I thought our hassle rate was sensational."

The vastly experienced Thwaites, who held her nerve superbly to score crucial goals late in the game in front of a noisy crowd at the M&S Bank Arena said the win was hugely satisfying.

"It was really tough we felt momentum swings switching but we managed to find another level," she said.

"I feel like it was really good how we played at times, but we have so much to improve on."

- AAP