Simmons was the surprise inclusion in Cheika's team, named today, for the must-win clash against New Zealand at Forsyth Barr Stadium.
The 28-year-old will start in the second row alongside Adam Coleman, pushing Rory Arnold to the reserves.
Simmons is coming off a lacklustre Super Rugby season and was recently released from his contract with the Queensland Reds, with a move to the NSW Waratahs expected to be made official in the coming weeks.
The 72-test veteran was also dropped twice last year by Cheika, including being sent back to play in the National Rugby Championship after the Wallabies were belted in the Bledisloe opener.
"It's an opportunity for Simmons to put his foot down now," Cheika told reporters in Christchurch.
"He's having a change in his own career now ... and I think it's time he puts a marker down for his international career as well in dominating that lock position.
"Saturday is the day to show that. He knows that as well. It's not anything I wouldn't say to him directly either. Saturday is the day for him to show up and say, 'yeah, this is what I can do.'"
Simmons' elevation was one of three changes made by Cheika from the team that lost 54-34 to the All Blacks last week.
Samu Kerevi has paid the price for his poor defensive display and is out of the match squad altogether, with Tevita Kuridrani replacing him at outside centre.
But Cheika admitted he may have done Kerevi a "disservice" by picking him too soon, with the Reds powerhouse having only recently recovered from an ankle injury.
The other change sees Dane Haylett-Petty, who has recovered from the bicep injury that kept him out of the first Test, come in on the left wing for last week's debutant Curtis Rona, who drops to the bench.
Cheika will finalise his bench after Friday's captain's run in Dunedin, with Lopeti Timani and Jack Dempsey battling it out for the same loose forward spot.
Australia must win on Saturday to avoid a 15th consecutive Bledisloe Cup series defeat.
Team: Israel Folau, Dane Haylett-Petty, Tevita Kuridrani, Kurtley Beale, Henry Speight, Bernard Foley, Will Genia, Sean McMahon, Michael Hooper (capt), Ned Hanigan, Adam Coleman, Rob Simmons, Allan Alaalatoa, Stephen Moore, Scott Sio. Reserves: Tatafu Polota-Nau, Tom Robertson, Sekope Kepu, Rory Arnold, Lopeti Timani/Jack Dempsey, Nick Phipps, Reece Hodge, Curtis Rona.