The defending Olympic champions started their campaign with a 48-0 win over Japan before they defeated China 26-10.

The Chinese pushed Australia, however the class of John Manenti's side shone through.

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The wins set up a crucial clash with the US to determine the winner of the pool.

The Americans are also unbeaten, however they were below their best as they claimed patchy wins over Japan and China.

Australia are already through to Friday night's quarter-final, while the semi-final and medal matches are on Saturday.

Australia have struggled throughout the past 18 months, however there were few signs of rust on the opening day of the Olympics.

Emma Tonegato was a standout, scoring a hat-trick in the win over Japan.

The Wollongong star raced clock to make it to Tokyo, having undergone a shoulder operation in February.

Her performances on Thursday, however, show she is at full fitness and ready to play a key role in Australia's search for gold.

"It's an awesome way to get those nerves out," co-captain Sharni Williams told Channel 7 after the win over Japan.

"We haven't played a lot of games, to come out there and get that first win is really awesome.

"Sevens is an amazing game. It's very fast, it's quick, if you miss a tackle it could be a try. Whoever shows up on the day is going to win."