The openside flankers will both start the Wallabies' tournament opener at Millennium Stadium in Cardiff, with Cheika replicating his decision from Australia's Rugby Championship-clinching win over New Zealand in August.
The Wallabies coach said the pure talent of the duo meant he had to select both to start, with Pocock starting at number eight in place of the injured Wycliff Palu.
"It's pretty hard not to pick one of them [Pocock and Hooper]," Cheika said.
"I'm not trying to claim there's any brilliant rocket science behind it.
"You've just got two very good players and the way they've played throughout the Super Rugby season and in the international season either together or separately has forced the coach's hands."
Australia are on their toes to start the World Cup, having seen South Africa suffer a shock defeat to Japan.
Cheika has named seven World Cup debutants for the clash, including Hooper, Israel Folau and Bernard Foley.
Will Genia will start for Australia for the first time since the Wallabies' win over South Africa in the Rugby Championship in July.
In some more good news for Cheika's side, Dominiko Waqaniburotu will miss the encounter due to a one-week suspension.
The 29-year-old was banned for a dangerous tackle in Fiji's tournament-opening 35-11 loss to England on Friday.
Fiji made four changes to the team that lost to the hosts, with Peceli Yato named to replace Waqaniburotu.
The Wallabies are one of four teams yet to start their World Cup, making the Pool A clash a potential danger game.
Australia do have a good record against Fiji, winning 16 of the previous 19 matches and losing just two.
Included in that run is 12 straight wins, the last of which came via a 49-3 result in Canberra five years ago.