The Waratahs defeated the Brumbies 28-13 in a spiteful encounter just three weeks ago in Sydney and another win would leave the titleholders' finals fate back in their own hands.
But less than pleased with his side's inability to put the Rebels to the sword after leading 13-0 early, Cheika said his charges would need to improve significantly to beat the Brumbies on their own patch for the first time since 2011.
"I don't think anyone's going to be shaking in their boots down there," Cheika said.
"There were some very bright patches in that game, in particular the first half, and there were some very dark patches as well when we lost our go-forward."
Fortunately for Cheika, a day after Wallabies and Waratahs coach admitted he was contemplating trying to lure the great George Smith out of retirement for the World Cup, Hooper responded to the challenge in similar fashion to how Brumbies breakaway David Pocock did on Friday night.
Cheika said he probably couldn't squeeze three openside flankers in his 31-man World Cup squad, placing pressure on Hooper and Pocock to deliver - and they did.
Hooper couldn't match Pocock's powerhouse hat-trick, but he still produced a priceless man-of-the-match display to ensure the Waratahs kept the plucky Rebels at bay.
"He is one of the most consistent footballers I have ever encountered," Cheika said.
"His consistency is ridiculous really."
Like all three of Pocock's tries in the Brumbies' 31-18 home win over the Highlanders, Hooper collected the opening five-pointer of the night in the ninth minute from the back of a Waratahs rolling maul.
He then ran a beautiful line off a Tahs lineout win before putting Ashley-Cooper over in the 20th minute.
A two-try hero in NSW's drought-breaking final win over the Crusaders, Ashley-Cooper returned to the scene of the Waratahs' greatest triumph to bag his first of the season.
But with Bernard Foley missing both shots at conversion and a penalty attempt, the Waratahs only led 13-3 at the break.
Two more long-range penalty goals from five-eighth Jack Debreczeni edged the Rebels to within four points of the Tahs - and effectively just a try from leapfrogging the defending champions on the ladder.
Horne's five-pointer on the hour gave the home team some breathing space but a 74th-minute try to Rebels reserve Bryce Hegarty, on for injured fullback Mike Harris, set up a heartstopping finish for Waratahs fans.
Rebels coach Tony McGahan was proud of his side's comeback but conceded their slow start ultimately cost them victory.
- AAP
