They finished the opening day of this tournament as one of five unbeaten sides.

America started their Pool C campaign by beating Samoa 26-12 before putting on a show fit for Sin City under the lights at the Sam Boyd Stadium to beat Australia 28-7 in a match they had led 21-0 at half-time.

They ran in four tries to one, including doubles for Martin Iosefo and Perry Baker, a former NFL player with Philadelphia Eagles, who scored his first try within the opening 60 seconds.

Another major shock in Pool D saw Argentina defeat New Zealand for only the second time in 82 matches. 

Argentina beat the All Blacks 26-19 and then followed it up by beating Scotland 21-19. 

"The last time we were very close and we talked about how we could do it," Argentina coach Santiago Gomez Cora said. 

"It’s just about not making any mistakes and playing very hard."

Earlier, New Zealand had beaten Uruguay 28-7.

It means New Zealand and Scotland, who beat Uruguay 40-14, will meet tomorrow for a place in the quarter-finals. 

Other countries unbeaten at the end of day one included the defending champions and current World Rugby Sevens Series leaders South Africa. 

South Africa erased a 14-0 deficit to defeat Wales 26-21 then closed the night with a 19-12 victory over Canada,

South Africa’s Pool B rivals England were also unbeaten, running in six tries in a 40-12 rout of Canada before a 33-12 win over Wales in which Tom Bowen scored a hat-trick.

South Africa and England are due to face off tomorrow to decide who finishes top of the Pool. 

Fiji, coming off a victory in the fourth leg of the series in Hamilton in New Zealand last month, thrashed Russia 38-0 and then followed it up and a 33-5 victory over France to top Pool A. 

South Africa, whose run to the Series title last season included a triumph in Las Vegas, lead the current standings on 77 points with New Zealand second on 69 and Fiji third on 62.