Ireland Under-20 head coach Mike Ruddock has made just one change to the side that won against Scotland in their final pool match - the versatile David Doyle starts in the back row.
Finlay Bealham and Alex Kelly have been named among the replacements for what is the sides' second meeting in eight days. The Baby 'Boks beat Ireland 42-26 in the pool stages.
Speaking ahead of the game, Ruddock said: "It's not that often that you get the opportunity to benchmark yourselves against the might of South Africa at this age grade and so having a second chance within eight days is rather unique.
"It is up to my players to put into practice the lessons learnt last time out. If we do that then we will improve our performance. If we improve on our last performance then we will be in the game big time."
IRELAND UNDER-20 Team & Replacements (v South Africa Under-20s, IRB Junior World Championship 5th-8th Place Play-Off, Stadio Plebiscito, Padova, Wednesday, June 22, kick-off 8.10pm local time/7.10pm Irish time):
15 - Tiernan O'Halloran (Galwegians/Connacht)
14 - Andrew Conway (Blackrock/Leinster)
13 - Brendan Macken (Blackrock/Leinster)
12 - Luke Marshall (Ballymena/Ulster)
11 - Andrew Boyle (UCD/Leinster)
10 - Paddy Jackson (Dungannon/Ulster)
9 - Kieran Marmion (UWIC/Exile)
1 - James Tracy (UCD/Leinster)
2 - Niall Annett (Belfast Harlequins/Ulster) (capt)
3 - Tadhg Furlong (Clontarf/Leinster)
4 - Michael Kearney (Clontarf/Leinster)
5 - Iain Henderson (Queen's University/Ulster)
6 - Eoin McKeon (Galwegians/Connacht)
7 - David Doyle (UCD/Leinster)
8 - Jordi Murphy (Lansdowne/Leinster)
16 - Finlay Bealham (Belfast Harlequins/Ulster)
17 - Conor Carey (Ballymena/Ulster)
18 - Daniel Qualter (Buccaneers/Connacht)
19 - Shane Buckley (Garryowen/Munster)
20 - Peter du Toit (UCD/Leinster)
21 - James McKinney (Queen's University/Ulster)
22 - Alex Kelly (UCD/Leinster)