Australia's Nick Malouf has scored after the siren to earn his country a quarter-final berth in a thrilling finish to day two of the Sydney Sevens at a heaving Spotless Stadium.
Needing to win by six points or more, Australia led 17-0 but then conceded 21 straight points to all but dash their hopes.
Australia rallied though, substitute Josh Coward scoring to lead by three before Malouf ran 60m to score the decisive try for a 29-21 win and set up a final-eight clash with series leaders Fiji on Sunday.
The opportunity to extend their lead only came about because South Africa, who finished top of the pool regardless, decided to run the ball after the siren in an attempt to win the game.
Australia managed to turn possession over, before Malouf skipped through several would-be tacklers and staggered to the line.
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The result left South Africa, Australia and Argentina on equal points, with the hosts surviving thanks to their slim three-point differential advantage over the South Americans.
The win ironically erased memories of a flat first-up defeat to Argentina that looked to have scuppered their title defence.
Australia were sloppy in the second half in a 29-14 loss to put the hosts behind the eight ball, before a 32-0 defeat of Tonga breathed life into their campaign.
"We knew we had to win by six and the boys knew too, it was a real moment to embrace and own and fair play they came up with the goods," said coach Tim Walsh, who rated it their best win since defeating the same opponent in last year's Sydney final.
"Luckily, well not luckily, we got an opportunity and we took it.
"We have to repeat the way we played today (against South Africa) for three games tomorrow."
Captain Lewis Holland scored a first-half double and said they deserved the positive result given their terrific response to the loss earlier in the day.
"The first game was about effort and that's what disappoints me the most. You can cop being beaten by a better team (but) effort doesn't take any skill," he said.
"It's not luck (to win after the siren), it's hard work ... across the board (against South Africa) just our energy and our effort was unreal."
Their miraculous win ensures both men's and women's sides remain in the hunt for back-to-back titles after the women beat France 21-17 in their Saturday afternoon quarter-final to set up a final four clash with Ireland.
