The Blitzboks were forced to dig deep in their Cup quarter-final encounter with Australia, eventually prevailing 17-14 to advance to the semi-finals.
They will now face the United States who fought back from a 0-19 half-time deficit to prevail 21-19 over Argentina. Fiji and England/New Zealand will contest the other semifinal after seeing off Canada and England/New Zealand, respectively.
In the Challenge Trophy division, France progressed to the semi-finals with a comfortable 24-14 victory over Japan and will meet Kenya, who held on to claim a 21-19 victory over Chile. Scotland came from 7-21 down to beat Wales 28-21. They will now meet Samoa in the other semi-final after they beat Russia 31-7.
South Africa 17-14 Australia
Australia took an early lead when they benefitted from a quickly taken penalty. They spotted a massive hole in the South Africans' defence to dot down under the posts. The conversion was successful and they held a 7-0 lead after two minutes.
The Blitzboks maintained their composure and kept the continuity going. The ball was spread wide to Ruhan Nel, who cut in-field and grabbed their first try under the posts. Cecil Afrika added the extras to level matters at 7-7 after four minutes.
And they nearly took the lead in the final minute of the half but Siviwe Soyizwapi was brilliantly tackled into touch, inches from the try-line as the teams remained deadlocked at the break.
The Blitzboks took the lead early in the second half when Soyizwapi spotted a gap and raced through to dot down. The conversion was missed but they led 12-7 after nine minutes.
Australia hit back two minutes later though when their converted try handed them a 14-12 lead with three minutes left to play.
However, with one minute on the clock, a quickly taken penalty by du Preez saw him send the ball to Rosco Speckman and he turned on the pace to sprint down the sideline and score the match-winning try.
Argentina 19-21 USA
Argentina grabbed the lead with a converted try before doubling their lead in the final play of the first half to head into the break, 14-0 in the lead.
The South Americans then made it 19-0 after they scored their third try after 30 seconds of play in the second half. The United States got themselves back in the game with two quick converted tries to trail 14-19 with three minutes to play.
The United States then grabbed a 21-19 lead in the 13th minute with a third seven-pointer and managed to close out the encounter to reach the semi-finals.
Fiji 31-12 Canada
It took Fiji three minutes to open the scoring with a converted try but Canada hit back from the restart to reduce the deficit to 5-7. Fiji finished the half strongly though as a two more converted tries handed them a 21-5 half-time lead.
Fiji stretched their lead to 26-5 with a converted try but Canada hit back with a converted score to trail 12-26. Fiji had the final say when they scored in the final play of the game to take a step closer to the Cup Final.
England 0-19 New Zealand
France 24-14 Japan
France were dominant in the first half as they had the wind at their backs. They managed to put some distance between them and Japan as they ran in three tries - one converted - to take a 17-0 lead. However, Japan had something to smile about as they grabbed a converted try with the final play of the half to trail 7-17 at the break.
The scoring dried up for the better part of the half but both sides were able to grab a try each to give the fans something to cheer about.
Kenya 21-19 Chile
The Kenyans' size and power proved too much for the Chileans to handle as they conceded three converted tries to trail 0-21 at the break.
Chile dominated the second half - keeping Kenya scoreless - and were rewarded with three tries of their own, two converted, to fight-back to trail 19-21 in the dying seconds. They retained possession from the kick-off but a handle error saw their chances of victory fade away.
Scotland 28-21 Wales
The sides exchanged early seven-pointers before Wales pulled ahead, 21-7 compliments of two further converted tries. Scotland edged themselves back into it with a converted try in the final play of the half to trail 14-21 at the break.
Scotland levelled matters at 21-21 early in the second half and then took a 28-21 lead with three minutes remaining in the contest. They managed to keep Wales scoreless to advance to the semi-finals.
Samoa 31-7 Russia
Samoa got the scoring going in the third minute to take a 7-0 lead, only for Russia to hit back and level matters two minutes later. Samoa closed the half on the front foot by adding a five-pointer to take a 12-7 lead at the break.
Samoa put some distance between themselves and Russia with two quick tries to extend their lead to 24-7 and secured the victory with the final play of the match by grabbing another converted try.
(Kick-off is local - GMT minus eight hours)
13th place semi-finals
Japan v Chile - 11.24
Wales v Russia- 11.46
Challenge Trophy semi-finals
France v Kenya - 12.08
Scotland v Samoa- 12.38
Australia v Argentina - 13.00
Canada v England - 13.22
South Africa v USA - 13.44
Fiji v New Zealand - 14.06
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