Australia, minus injured skipper Meg Lanning, have set South Africa a victory target of 270 runs in their final Women's Cricket World Cup group match in England.
Stand in captain Rachael Haynes won the toss and opted to bat on Saturday in Taunton, with Alex Blackwell her deputy.
Openers Beth Mooney and Nicole Bolton put on 114 for the first wicket.
Mooney was the first to be dismissed for 53 off 58 deliveries. She was followed three runs later by Haynes who was caught-and-bowled for a duck.
Bolton was out for 79 (87 balls) to leave Australia at 3-154, before Elyse Villani also fell for a duck with no change to the total.
Ellyse Perry and Blackwell steered the Aussie women out of trouble. Perry's great form with the bat continued, eventually falling for 55 from 58 balls after hitting seven fours.
Blackwell made 33 before Australia lost quick wickets to be bowled out for 269 in 48.3 overs.
Sune Luus was the pick of South Africa's bowlers, taking 5-67 off her 10 overs.
Lanning was ruled out of the last pool match due to her long-standing shoulder injury.
After scoring a match-winning 76 on Wednesday against India, she sat out the South African clash to preserve her for next week's semi-finals and then potentially the final on Sunday week at Lord's.
Australia are aiming to inflict some early psychological blows on the Proteas ahead of a probable semi-final between the teams on Thursday in Derby.
Both sides have already secured their spots in the last four.
Australia are aiming to win the World Cup for an unrivalled seventh time.
