Australia forward Mitchell Duke said "bring on whoever" when asked about taking on Lionel Messi or Robert Lewandowski in the World Cup round of 16.

The Socceroos progressed to the knockout stage of a World Cup for only the second time in their history, 16 years on from first doing so in 2006, by beating Denmark 1-0 on Wednesday.

Australia's victory at Al Janoub Stadium was required, with Tunisia stunning a much-changed France side in Group D's other game.

Messi's Argentina or Lewandowski's Poland are the most likely candidates to face Australia on Saturday, though Saudi Arabia could yet sneak through as Group C winners.

But whoever Australia have to face, Duke said they will be ready.

"Bring on whoever, I feel like we could take on anyone right now," he told reporters. "That's the belief, we go out with that mentality.

"Don't write us off. You can see there's something special building here, there's lot to be excited about."

Duke, who scored Australia's winner against Tunisia on matchday two, wants to make more history in Qatar, with the 31-year-old adding: "It doesn't really feel like it's sunk in quite yet.

"That's what some of the boys were saying when they walked in. 'Do we realise what we've just done?'

"Playing a part in history right now, we've got two clean sheets, six points out of a group with two world class teams. It's unbelievable, a lot of people would have written us off but the belief in our team is unbelievable.

"Everyone wrote us off, we've finished second in the group, it's massive and we're not done yet – we want to make history."

Australia captain Mat Ryan added that the team's unity is what has pushed them to successive World Cup wins for the first time.

"The pride of the whole group, we have such a great team – youngsters, leaders," Ryan said.

"The togetherness is our backbone, our identity and the foundation. The world keeps giving us reasons to be proud of ourselves.

"It's great to see we’re an ambitious group. We're enjoying the victory but the comments are already coming out – we want to keep going, keep having victories like this and go as deep as we can, make the nation as proud as we can.

"Everything's a collective, from front to back, the commitment from everyone. The ones who haven't got on yet, the ones who have, the ones who haven't played as much as the others, the mentality and attitude has been top class and that's what we strive for. Everyone sets the standards high."