The winners of the match at Twickenham on Saturday will top the group and get an easier draw in the knockout stages.
"Matt as a second playmaker is one of the best in Europe, if not the world," Roberts told reporters.
"He is a special player and I’m sure he is delighted at the chance to play for Australia again. We have to do a job on him. We have to put him under pressure and stop their speed of ball, which is difficult to defend against, as England found out."
Wales have lost their last 10 matches against Australia but many of them have been extremely close.
"Looking back over the last seven years it’s the same old story," Roberts said.
"Over the last 10 minutes, they have killed us on many occasions. I hope that what is on the line on Saturday will bring out the best in us."
Roberts nervously watched Australia beat England 33-13 on Saturday, a result that sent Wales through to the quarter-finals.
"I was shaking for 80 minutes," he said. "It was like playing a game, though not expending as much energy. It was a bit awkward being surrounded by a load of English. When it got to 20-13, I’m sure the whole of Wales was panicking a bit.”
Wales assistant coach Rob Howley is relishing the challenge of pitting his wits against the Wallabies.
"You look forward to playing and coaching against Australia," he said.
"As for the manner of the defeats over the last two or three years in particular, the margins are pretty low -- one to five points. History is pretty irrelevant in World Cups and it’s about the side who can master the moments and have accuracy in the last 20 minutes of the game."
Wales showed great composure in the closing minutes to seal their dramatic 28-25 win over England and must do the same again.
"We need to be more accurate against Australia," Howley said. "We need to start well and get on the scoreboard.”
(Reporting by Ed Osmond, editing by Nick Mulvenney)
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