Timani gets first Wallabies start
Timani pipped Leroy Houston, who was added to the squad for the historic clash, to the starting spot after the pair were in a tight race to fill the No.8 jersey left by Sean McMahon.
McMahon suffered an ankle injury in their 10-1 defeat to the Springboks in Round Five and is set to be on the sidelines for up to a month.
Houston could yet be among the replacements, with Wallaby coach Cheika due to name his bench on Friday.
The only other change to the starting line-up sees Timani's fellow Test novice Rory Arnold selected in place of Rob Simmons to partner Adam Coleman in the second row.
Simmons passed concussion protocols after the defeat by the Springboks but has been left out as Cheika tries to find his premier lock combination.
Victory for Australia, allied to a New Zealand win over South Africa, would see the Wallabies finish runners-up.
Saturday's match at Twickenham is a repeat of last year's World Cup semi-final at the London ground, which saw Australia beat Argentina 29-15.
Their replacements will be named on Friday, October 7.
Australia - Revised: 15 Israel Folau, 14 Dane Haylett-Petty, 13 Samu Kerevi, 12 Bernard Foley, 11 Reece Hodge, 10 Quade Cooper, 9 Will Genia, 8 Lopeti Timani, 7 Michael Hooper, 6 Dean Mumm, 5 Adam Coleman, 4 Rory Arnold, 3 Sekope Kepu, 2 Stephen Moore (captain), 1 Scott Sio
Replacements: 16 James Hanson, 17 Tom Robertson , 18 Allan Alaalatoa, 19 Kane Douglas, 20 Scott Fardy, 21 Leroy Houston, 22 Nick Phipps, 23 Tevita Kuridrani
Date: Saturday, October 8
Venue: Twickenham, England
Kick-off: 18.30 (15.30 ART; 05.30 AEDT, Sunday, October 9)
Referee: Mathieu Raynal (France)
Assistant referees: JP Doyle (England), Matthew Carley (England)
TMO: Rowan Kitt (England)