Reece Walsh has hit back at critics who claimed Australia's forwards had been outmuscled ahead of the Kangaroos' World Cup semi-final against Samoa. 

The fullback has retained the No.1 jersey for Sunday night's semi-final against Samoa at Allianz Stadium, with James Tedesco named on an extended six-man bench.

But ahead of the match, Walsh has took issue with those who have suggested Australia's forwards have not done enough in previous fixtures. 

Fans have been scathing of the Kangaroos forwards and have warned that if they do not lift, a shock early exit is on the cards.

'Australia will need to be very disciplined or Samoa will run through them,' one posted.

'Lol they’ll be absolutely outmuscled in the forwards,' added another.

'Critics are right our middle has been soft,' a third wrote.

Walsh said the criticism had been disrespectful to Australia's forwards. 

'I feel like our forward pack's been disrespected a lot this tournament,' he said.

'There's a lot of talk about the other teams. They're great players. They're awesome players, don't get me wrong.

'But the way that this pack works their a*** off for us, they're the reason why we're winning these games and the reason why we're working so hard. The passion they play with and the hard work, the kick chase, the small details.'

Australia are unbeaten heading into the semi-finals, but their journey has seen uncomfortable moments against both New Zealand and Fiji.

The Kangaroos edged New Zealand 24-22 in their opening match before overcoming Fiji 36-22, with the latter performance prompting a blunt assessment from Sydney Roosters coach Trent Robinson. 

'Australia got outmuscled by Fiji and they did by New Zealand last week,' Robinson said in commentary.

'It doesn't matter what halves pair you play… can they win the forward battle? Can they create enough of a platform?

'Australia needs to muscle up more than what they did in the first two Tests. They need to get a hell of a lot better there.'

Robinson said Fiji's challenge had lasted well beyond the opening exchanges.

'They were losing in the 60th minute, not just in the 20th minute. Fiji outmuscled them in how they carried the ball and how they tackled.'

Walsh subsequently starred in Australia's 66-6 demolition of the Cook Islands, scoring a try and delivering five try assists.

He credited the pack for laying the platform and said some of their most valuable contributions were being overlooked. 

'It's something that the fans and you guys [media] probably don't see, but we see and that's one thing I see with these other teams,' he said.

'When they're looking at us, they know the strengths that we bring. 

'All credit to them, they're awesome packs but I love these boys and how hard they work because those little efforts... we appreciate them so much.'

Forward Liam Martin has also made it clear the criticism had registered inside Australia's camp.

'We all know that we haven't played our best game, but the really exciting thing is we know we've got so much improvement in us, so if we bring our best game, I don't think anyone can match us,' Martin said.

'You've got to have that mentality of taking it to them and when people criticise you and say that you know they've got it over you. We take it pretty personally.'

Walters has now entrusted Walsh with the starting fullback role for Australia's biggest match of the tournament, despite Tedesco entering the World Cup fresh from helping the Roosters win the NRL premiership.

Walsh had spent the roughly two months sidelined with an ankle injury, but his performances in the green and gold have earned him the nod.

There was another significant selection call in the centres, where Bradman Best retained his place ahead of Latrell Mitchell.

Mitchell and Tedesco were named on an extended interchange alongside Ethan Strange, Keaon Koloamatangi, Cameron Murray and Reuben Cotter, while Tom Dearden and Cameron Munster retained their places in the halves. 

Australia now face a Samoa side coming off a bruising encounter with Tonga, with Walters warning his players that their strongest performance is required.

'Samoa were very impressive in a physical battle which had a lot of emotion last weekend against Tonga and we know we are in for a tough contest on Sunday night,' Walters said.

'It's going to be a great occasion in front of a full house at Allianz Stadium, and we've got to meet the occasion with our best performance of the tournament.'

Samoa have made one enforced change, with Ronald Volkman replacing Chanel Harris-Tavita at five-eighth because of a hamstring injury.

In the other half of the draw, Kalyn Ponga's inclusion in New Zealand's extended squad has raised the prospect of another showdown with Walsh should both nations reach the final.

Ponga was named just 22 days after breaking his forearm in the tournament opener against Australia, although Keano Kini remains the starting fullback for Saturday night's semi-final against Tonga in Newcastle.