The others see Pekahou Cowan included to start at loosehead prop, in the place of Salesi Ma'afu, after coming off the bench as a hooker against Gloucester.
Ma'afu is relegated to the bench, after featuring on the tighthead side of the scrum at Gloucester, with Sekope Kepu switching from loosehead to tighthead to accommodate the inclusion of Cowan.
James O'Connor also starts at fullback with Kurtley Beale, who filled that role against Gloucester, switching to wing in the place of Drew Mitchell.
O'Connor is one of seven players in the starting XV who back up from last weekend's Test match in Edinburgh, although centre Ryan Cross is the only player who starts at Cardiff who also featured in the run on list for the Test match.
Kepu, Hooker Tatafu Polota-Nau, No 8 Richard Brown, halfback Luke Burgess and lock Dean Mumm are the other starters playing their second match in four days.
Mumm again leads the midweek side, after making a successful fist of his first time in charge when Australia over-powered English Premiership side Gloucester 36-5 at Kingsholm earlier in the month.
Bench inclusions lock Mark Chisholm, flanker George Smith and inside centre Quade Cooper all started in the 8-9 loss to Scotland at the weekend.
The bench also sees the inclusion of squad newcomer Luke Morahan, who joined the team last week in Edinburgh as the replacement for Stirling Mortlock.
Morahan was denied the opportunity to join Toomua at the Under-20 World Cup in Japan earlier in the year due to injury, after having been included in the training squad.
The Queensland teenager has excelled for Australia on the IRB Sevens circuit, and now has the chance to represent his country at senior level.
His state colleague, halfback Richard Kingi, is also on the bench and is also poised to play for his country at senior level for the first time, albeit in a non-cap match.
Kingi, who has played for Australia in Sevens and was brought on this tour for development purposes, is the only member of the originally named touring group who has yet to have taken the field on the trip.
15. James O'Connor (Western Force) 14. Lachie Turner (NSW Waratahs) 13. Ryan Cross (Western Force) 12. Tyrone Smith (Brumbies) 11. Kurtley Beale (NSW Waratahs) 10. Matt Toomua (Brumbies)
9. Luke Burgess (NSW Waratahs)
8. Richard Brown (Western Force) 7. Matt Hodgson (Western Force) 6. Mitchell Chapman (Brumbies) 5. Dean Mumm (NSW Waratahs, captain) 4. Dave Dennis (NSW Waratahs) 3. Sekope Kepu (NSW Waratahs) 2. Tatafu Polota-Nau (NSW Waratahs) 1. Pekahou Cowan (Western Force)
16. Salesi Ma'afu (Brumbies) 17. Matt Dunning (Western Force) 18. Mark Chisholm (Brumbies) 19. George Smith (Brumbies) 20. Richard Kingi (Queensland Reds) 21. Quade Cooper (Queensland Reds)
22. Luke Morahan (Queensland Reds)