The Australians started nervously, with several handling errors, and Samoa opened the scoring, Motu Opetai intercepting a long pass to run most of the length of the pitch.
But Australia hit back just before half time, with Henry Hutchison smashing through a rare Samoan missed tackle to level the scores at the break.
A Nathan Lawson try in the corner doubled Australia's advantage halfway through the second half, accurate long passing stretching the Samoan defence.
Hutchison touched down his second try with seconds to go as the Samoan defensive effort took its toll on their fitness. Faafoi Falaniko nabbed a consolation try right at the death.
France are the team to beat in the men's competition, with superstar Antoine Dupont one of the pin-ups of the Games and arguably the world's best 15-a-side rugby player.
But Fiji have won both Olympic Golds since the sport was introduced at the Rio Games in 2016 and will be difficult to beat despite a poor season by their standards.
Fiji and France were drawn together in Pool C and will face each other in a mouthwatering clash on Thursday. The other two teams in the pool are United States and Uruguay.
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.
