Rugby World Cup 2015: Australia are Wales' 'biggest challenge'

Jamie Roberts has played in five of Wales' last 10 defeats against Australia

Wales will face one of the World Cup's best attacks when they play Australia on Saturday, says centre Jamie Roberts.

The Wallabies backs crafted three superb tries in their 33-13 win against England and Roberts says Wales know the size of the challenge at Twickenham.

"When they get things right in attack they are one of the world's most dangerous teams," the 28-year-old said.

"This is going to be the biggest defensive challenge we've faced over the last few months, if not year."

Australia and Wales have both reached the quarter-finals, with this weekend's match deciding who finishes top of Pool A.

The group winners are likely to face either Scotland or Japan next, with South Africa the expected opponents for the runners-up.

Australia's strength in depth

Australia will be without open-side flanker Michael Hooper, 23, who has been suspended after a disciplinary hearing found him guilty of an illegal shoulder charge on England's Mike Brown.

The Wallabies are also likely to be without wing Rob Horne and have an injury worry over full-back Israel Folau, who has a sore ankle.

But Roberts says the absentees are unlikely to hinder Saturday's opponents.

"Hooper is one of their best players and he's not playing, so certainly it's good for us," said Roberts.

"But the depth in their squad is fantastic and whoever comes in and plays in the back-row now I'm sure is going to be a really good player.

"Folau is a special player, attacking threat - his abilities as an athlete are pretty frightening and he's a special player if he's put in space.

"But they have Drew Mitchell to come in for Horne, and he's a special player in his own right.

"This backline we'll be facing is probably the most formidable backline in the tournament."

Israel Folau scored two tries against Wales in November's 33-28 win in Cardiff

11th time lucky?

Roberts has painful and happy memories of his first meeting with Australia in 2008.

He suffered a fractured skull after an accidental clash of heads with Stirling Mortlock in the opening minutes in Cardiff that year, but played a big part in Wales' opening try before leaving the field.

The home side went on to win that game 21-18 - but have lost 10 consecutive meetings with the Wallabies since.

"I only lasted about 10 minutes but that was the last time we beat Australia," he said.

"You look back at the last seven years and it's the same old story, the last 10 minutes has killed us on many an occasion and we're hoping the occasion on Saturday and what's on the line will bring out the best in us for the full 80 minutes."

Chance to play open rugby

With both teams having already qualified for the quarter-finals, Roberts suggested Wales could be given a little more freedom in their play.

"We have gone into games with Fiji, England and Uruguay with certain game plans - now we face Australia knowing we've qualified, I hope maybe we can go out and play a bit more open rugby and really express ourselves," he added.

"We're playing at Twickenham, it'll be a sell-out on Saturday and the atmosphere there at the moment is pretty incredible.

"To play in front of that many Welsh fans away from home is incredible and the game will be an incredible spectacle knowing both teams have qualified."