Ireland U20s have made four changes to the starting XV that played out a 34-34 draw with England U20s on Saturday, ahead of Thursday's clash with Australia U20s (kick-off, 10.00am).
Hugh Cooney has been suspended following his red card against England, with Hugh Gavin moving to centre and James Nicholson coming onto the left wing.
In the pack, tight-head Ronan Foxe will make make his U20s debut, with Charlie Irvine coming into the second-row, and Brian Gleeson coming back in at number eight.
On the bench, Danny Sheahan, Jack Oliver, Harry West, and Rory Telfer come into the squad.
Australia have made 10 changes to the side that defeated Fiji 46-37 in their opening game.
A loss to the Aussies means Ireland will almost certainly be eliminated from semi-final contention, while a win would likely see them top the group or at least put them in pole position for the best runner-up spot in the last four.
"It has been a quick turnaround from Saturday but we were able to turn the page positively, and learn from our first outing of the tournament," said head coach Richie Murphy.
"We know the very nature of this World Rugby U20 Championship is that the big games come thick and fast and facing the Junior Wallabies is another huge test for our group. We’re looking forward to the challenge."
Ireland U20s And Australia U20s Set For Defining Showdown
15. Henry McErlean (Terenure/Leinster)
14. Andrew Osborne (Naas/Leinster)
13. Hugh Gavin (Galwegians/Connacht)
12. John Devine (Corinthians/Connacht)
11. James Nicholson (UCD/Leinster)
10. Sam Prendergast (Lansdowne/Leinster)
9. Fintan Gunne (Terenure/Leinster)
1. Paddy McCarthy (Dublin University/Leinster)
2. Gus McCarthy (UCD/Leinster)(captain)
3. Ronan Foxe (Old Belvedere/Leinster)*
4. Charlie Irvine (Queen’s University/Ulster)
5. Conor O’Tighearnaigh (UCD/Leinster)
6. James McNabney (Ballymena/Ulster)
7. Ruadhan Quinn (Old Crescent/Munster)
8. Brian Gleeson (Garryowen/Munster)
16. Danny Sheahan (UCC/Munster)
17. George Morris (Lansdowne/Leinster)
18. Fiachna Barrett (Corinthians/Connacht)
19. Evan O’Connell (UL Bohemians/Munster)
20. Diarmuid Mangan (UCD/Leinster)
21. Jack Oliver (Garryowen/Munster)
22. Harry West (Buccaneers/Connacht)
23. Rory Telfer (Queen’s University/Ulster).
*Denotes uncapped at U20 level
1. Jack Barrett (NSW Waratahs, Randwick)
2. Max Craig (QLD Reds, Easts Tigers)
3. Massimo De Lutiis (ACT Brumbies, Western District Lions)
4. Jhy Legg (Western Force, Wests Scarborough)
5. Daniel Maiava-Tapusoa (Melbourne Rebels, Wests Bulldogs)
6. Lachlan Hooper (ACT Brumbies, Vikings Rugby)
7. Ned Slack-Smith (Western Force, Palmyra Rugby Union Club)
8. John Bryant (QLD Reds, Souths Magpies)
9. Teddy Wilson (c) (NSW Waratahs, Eastern Suburbs)
10. Jack Bowen (NSW Waratahs, Eastern Suburbs)
11. Darby Lancaster (Melbourne Rebels, Eastern Suburbs)
12. David Vaihu (Melbourne Rebels, Wests Bulldogs)
13. Henry O'Donnell (NSW Waratahs, Northern Suburbs)
14. Tim Ryan (QLD Reds, Brothers Rugby Club)
15. Mason Gordon (Melbourne Rebels, Wests Bulldogs)
16. Liam Bowron (ACT Brumbies, Canberra Royals)
17. Harrison Usher (QLD Reds, Bond University)
18. Nick Bloomfield (QLD Reds, Easts Tigers)
19. Toby Macpherson (ACT Brumbies, Uni-Norths Owls)
20. Leafi Heka Talataina (Melbourne Rebels, Endeavour Hills)
21. Klayton Thorn (ACT Brumbies, Gungahlin Eagles)
22. Harry McLaughlin-Phillips (QLD Reds, Souths Magpies)
23. Taj Annan (QLD Reds, Souths Magpies)