The hosts needed to beat the defending overall champions by five points to guarantee their place in the knockout stage at the Spotless Stadium.

Australia, leading 24-21 in overtime, launched a counter-attack after South Africa had failed to convert a penalty and Malouf went over to secure the win and a place in the last eight.

South Africa topped Pool D, despite the defeat, and are set to play England in the quarter-finals, while Australia set up a clash with Olympic champions Fiji.

The Fijian team, seeking a third straight win on this season's circuit, won all three of their matches in Pool A.

Fiji began with a 29-5 win over Japan before they overcame England 14-7 and Samoa 22-12.

The United States continued their strong start to the campaign as they finished top of Pool B with a 100 per cent record.

Spain, second in Pool C behind New Zealand, await for the US in the last eight.

The other quarter-final is due to see Pool C winners New Zealand face France.

In the women's competition, Ireland reached the semi-finals for the first time after they beat Spain 22-7.

Ireland will go up against defending champions Australia in the last four after the hosts maintained their perfect record with a 21-17 win over France.

New Zealand, bidding for a sixth consecutive series crown, also progressed to the semi-finals by defeating Canada 17-7 in a scrappy last eight contest.

The US are due to play New Zealand for a place in the final as they edged a low-scoring affair with Russia 7-5.

Both the men's and women's tournaments are set to conclude tomorrow.