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.

Portugal became ragged, giving away possession cheaply and Wallaby captain Porecki punished them again, touching down from the back of a short-range driving maul.

And before Portugal were back up 15 men again, prop Bell launched himself at the line from close in to score Australia's third try.

Once they had their full contingent back, the enterprising Portuguese were again the better side.

Portugal thought they had scored a richly deserved second try but Wallaby full-back Andrew Kellaway's last-ditched tackle forced flanker Nicolas Martins into touch before he dotted down, leaving Australia 24-7 up at the break.

Verve and panache

Australia secured the attacking bonus point seven minutes into the second period after another Portugal penalty allowed them to kick deep into their opponents' 22 before Mark Nawaqanitawase was able to pop the ball off for flanker McReight to score.

Donaldson missed the conversion but Australia were well in control against their spirited opponents.

Yet Portugal continued to play with verve and panache and thought they had scored again when hooker Mike Tadjer was driven over, but he was ruled to have knocked on in the grounding.

Wallaby replacement hooker Matt Faessler was yellow-carded for an infringement in the driving maul but Portugal couldn't capitalize and knocked on again metres from the line.

But then Wallaby replacement center Samu Kerevi was sin-binned for a forearm smash into Bettencourt's head and Australia were playing with 13 men.

Portugal kept coming and eventually, they drove Australia back from a five-metre scrum and Rafael Simoes touched down.

Australia had the last word as Marika Koroibete plowed over late on for their fifth try.