France struggled to live up to pre-tournament billing as favourites for Olympic Gold in rugby sevens on Wednesday, held to a 12-12 draw by the United States to the disappointment of a packed Stade de France.

Meanwhile, double Olympic champions Fiji burnished their own title credentials, swatting aside Uruguay 40-12 with typical Fijian flair.

The Les Bleus side featuring Antoine Dupont, arguably the world's greatest 15-a-side player, were left to rue several errors in possession that opened the door for their lesser-ranked opponents.

France opened their account halfway through the first half, a brilliant offload out of contact releasing Jordan Sepho for a try in the corner.

But the home crowd was stunned into silence just before the half-time whistle as US flyer Lucas Lacamp broke through the French defence for a long-range effort that earned his team a 7-5 lead at the break.

France restored their advantage practically from the kick-off in the second half, Rayan Rebbadj powering over after a move that started with a clever Dupont offload.

But a powerful American counter-ruck after France were caught isolated deep in their half allowed Marcus Tupuola to stroll in for a try that secured them a deserved draw.

"We lacked precision, especially close to the try line. We were knocked back a lot, especially at the start of the match," said France captain Paulin Riva.

"We didn't manage to finish, messed up every time we should have finished," he added.

The result blows open pool C, which also features Fiji, always a force in sevens despite a disappointing season by their standards.

With trademark free-flowing rugby, the Fijians had far too much pace and power for Uruguay, a Joji Nasova first-half double killing off the match as a contest before the break.

The South Americans put up a spirited effort, however, with two tries of their own but were no match for Fiji who laid down an impressive marker to the rest of the field.

Earlier, Australia squeezed past a determined Samoa side 21-14, courtesy of a Henry Hutchison double to get their pool B campaign off to a winning start.

The other pool B match saw Argentina roundly booed by the home faithful before running out comfortable 31-12 winners against Kenya.

France were billed as the team to beat in the men's competition, with superstar Dupont one of the pin-ups of the Games.

But Fiji have won both Olympic Golds since the sport was introduced at the Rio Games in 2016 and showed they will be no pushover.

Fiji and France will face each other in a mouthwatering clash on Thursday.

In what is a wide-open tournament for the men, stiff competition will also likely come from traditional rugby powers New Zealand, South Africa, Argentina, and Ireland.

With the global exposure that comes with the Olympics and playing to a sold-out Stade de France, World Rugby's chief executive Alan Gilpin has described the tournament as a "coming of age" moment for the sport.

"There has never been a greater spotlight on the sport," Gilpin said ahead of the competition.

The women's tournament starts on Sunday, with Australia and New Zealand well-placed to battle for the gold. (AFP)