Aussies beaten in Sevens semis

Australia have failed to back up their shock win over South Africa at the Singapore Sevens, belted by the United States 40-7 in the semi-finals on Sunday.

Aiming to qualify for their first final of the world series this season, Australia missed a whopping 17 tackles in the six-tries-to-one defeat.

Australia opened the scoring with a clever John Porch try in the second minute before the US completely dominated proceedings, enjoying a glut of possession helped by skilful execution at the restarts.

In the tournament decider, the US will face Canada who upset England 17-5 in the other semi.

Earlier, Lachie Anderson scored a last-minute try as Australia stunned world series leaders South Africa 19-17 in the quarter-finals.

Anderson took a one-handed Liam McNamara offload with 20 seconds remaining to sprint over under the posts for the decisive five-pointer, with Porch's conversion capping the big comeback victory.

Australia were 10-0 down after just two minutes but fought back through tries to Simon Kennewell and captain Tom Lucas.

The defeat for the Blitzbokke meant the eighth round of the world series would be the first time South Africa wouldn't appear in the tournament decider.

The US upset Fiji, who claimed the Hong Kong Sevens title last weekend, in a 24-19 quarter-final triumph.

Australia will be aiming to equal their best result of the season, a third place finish in Hong Kong, when they battle England in the bronze playoff at 10.05pm AEST.