Fiji took top-spot off the USA at Twickenham and are two points clear going into the final round of the HSBC World Series, next weekend in Paris.
The Americans comprehensively won their bronze-medal match against France, 31-14.
This meant the Pacific Islanders needed a win over Australia to ensure the World Series is in their hands upon arrival in the French capital.
They delivered, thrashing the men in Green and Gold (43-7), running in seven tries in the process.
Fiji head coach Gareth Baber said: “We found it tough in the first four or five minutes when Australia put something in.
“We knew they are a good side and tough to play against – so we needed to get some scores on the board, and we did it with some style.”
All the automatic qualification places have now been filled – Fiji, USA and New Zealand will be joined in Tokyo by South Africa.
The Blitzboks lost two games on Sunday but due to England’s failings, have guaranteed themselves the chance to fight for Olympic glory in 2020.
England can secure Great Britain’s Olympic rugby representation via European qualifying in July.
England coach Simon Amor spoke of how proud he was with his young side’s performance and bravery.
“We’d shown such incredible fight and effort right the way through this tournament,” said Amor.
“I’m really proud of the performances the guys put in – some narrow losses but there are ups and downs of sevens and that is what the game is about.”
“For those young guys to come through that is encouraging and exciting for us, we just didn’t get it right in that last one.
“I think up to 10 of our squad is out injured at the moment so it’s really stretching us, and we’re having to delve into the youngsters.”
The Welsh have eased fears of relegation after a crucial 17-0 win over their nearest rivals, Japan.
They now sit in 13th place going into Paris, where Kenya and Japan will be nipping at their heels, all battling to ensure they are World Series regulars again next campaign.
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