Australia coach Michael Cheika has said that "rocket science" was not required in his decision to select both Michael Hooper and David Pocock for the Wallabies' opening Rugby World Cup fixture against Fiji.

Both Hooper and Pocock are recognised openside flankers, with Pocock moving into the number 8 berth for the Fiji clash.

"It's pretty hard not to pick one of them. It sort of means you pick them both. I am not trying to claim there is any brilliant rocket science behind it. You just have two very good players," Cheika told reporters ahead of Wednesday night's match.

"The way they have played throughout the Super Rugby season and in the rugby internationals, either together or separately, has forced the coach's hand - and that is exactly what you want from players."

Fiji coach John McKee, who's side were beaten by England in their opening tie, added: "We suspected Australia would go with Hooper and Pocock in the back row. That was the combination that was so successful in the Bledisloe Cup game in Sydney (against New Zealand) just over a month ago, so they have gone with that again and it gives them good mobility in the back row."

The Wallabies, who play Fiji at the Millennium Stadium on September 23, will also face Pool A ties against both England and Wales, as well as bottom side Uruguay.