O’Mahony is joined in the back row by CJ Stander at blindside and Jack Conan at Number Eight.
James Ryan and Devin Toner continue their partnership in the second row while Jack McGrath and Sean Cronin join Tadhg Furlong in the front row.
In the backline, Robbie Henshaw reverts to outside centre with Bundee Aki lining out in the No. 12 jersey. Conor Murray and Johnny Sexton fill the halves. Rob Kearney, Jacob Stockdale and Keith Earls make up the back three.
The replacements named are Niall Scannell, Cian Healy, John Ryan, Tadhg Beirne, Jordi Murphy, Kieran Marmion, Ross Byrne and Jordan Larmour.
Rob Herring, Andrew Porter, Dan Leavy, Garry Ringrose Andrew Conway, John Cooney and Joey Carbery all fall out of Joe Schmidt’s matchday 23. Leavy, Ringrose and Conway are out through injury.
The series is currently tied at one win each, with Australia edging Ireland 18-9 in the first Test and Ireland responding with a 26-21 win in the second Test.
1. Jack McGrath, 2. Sean Cronin, 3. Tadhg Furlong, 4. James Ryan, 5. Devin Toner, 6. CJ Stander, 7. Peter O’Mahony (C), 8. Jack Conan; 9. Conor Murray, 10. Johnny Sexton, 11. Jacob Stockdale, 12. Bundee Aki, 13. Robbie Henshaw, 14. Keith Earls, 15. Rob Kearney.
Reserves: 16. Niall Scannell, 17. Cian Healy, 18. John Ryan, 19. Tadhg Beirne, 20. Jordi Murphy, 21. Kieran Marmion, 22. Ross Byrne, 23. Jordan Larmour.
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