Australia kept their faint hopes of reaching the Rugby World Cup knockout stages alive with an unconvincing 34-14 victory over minnows Portugal on Sunday.

Tries from forwards Richie Arnold, David Porecki, Angus Bell, and Fraser McReight, and winger Marika Koroibete secured Australia a bonus point and a Pool C lifeline, while Portugal hit back through Pedro Bettencourt and Rafael Simoes.

The Wallabies can still reach the quarter-finals if Fiji loses to Portugal next week without a bonus point.

"It was good, the boys dug deep knowing it could be our last game, and credit to Portugal, they are a very solid team," Australia's No.8 Rob Valetini said.

"We pride ourselves on the forwards trying to get over their forwards. A lot of things we did at training transferred over to the field, we knew the game was going to be won by the forwards."

It was a poignant night for Wallaby prop James Slipper, who broke his country's record for the most caps at a World Cup.

"I think we are really proud of what we gave, but it is a loss. I am proud, but not happy to be honest," said Portugal captain Tomas Appleton.

"We still have one more shot to show what we can do next week, but we are a bit disappointed."

Portugal showed a fearlessness to run the ball from the get-go, even from deep inside their own half.

Despite an early penalty from Australia's Ben Donaldson, Portugal deservedly took the lead when playing with a penalty advantage.

A slick back move set center Bettencourt free on the overlap to dive over in the corner.

Samuel Marques converted but moments later Bettencourt hit his opposite number Izaia Perese with a high tackle and was sent to the sin-bin.

Donaldson missed the resulting penalty but Australia soon made the extra man count with Valetini offloading to lock Arnold to score next to the posts.