Australia will meet New Zealand in the final of the Netball Quad Series in Cape Town, having continued their unbeaten run with a 65-48 win over hosts South Africa.
The Diamonds had already qualified for Wednesday's final (3am Thursday AEDT) courtesy of back-to-back victories over England and New Zealand.
Stacey Marinkovich's side had started slowly in their two previous Quad Series matches but despite resting leadership pair Liz Watson and Steph Wood - who had starred in Sunday's 59-57 victory over the Silver Ferns - they led at each change against the Proteas.
Ash Brazill, back in the side for her first series since returning to the AFLW, shone for the Diamonds with a high-energy performance at wing defence.
Star shooter Sophie Garbin, who finished with 32 from 36, sat out the final quarter after being floored by a heavy hit from South Africa's goalkeeper Phumza Maweni during the third period.
Garbin was replaced by Cara Koenen, who made the most of her time on court by shooting nine from nine.
Despite Koenen's strong showing, coach Marinkovich will hope the 25-year-old Garbin recovers in time for what promises to be a hard-fought final against World Cup holders New Zealand.
The Diamonds will face their old rivals from across the Tasman to determine the outcome of the series, after the Silver Ferns overcame sloppy England 55-45.
The Roses, who have failed to win a match in the series, led with 11 minutes to go but conceded 13 of the last 17 goals of the game to lose by 10.