Scrum-half Youngs came off the bench to score the decisive try in the win over Argentina last weekend while Flood was among the unused replacements. Now both will start against Georgia, with club colleagues Dan Cole and Manu Tuilagi retaining their places in the team.
Tom Croft is among the replacements as Tom Woods starts in the back row, and Louis Deacon sit out as Simon Shaw and Tom Palmer come into the second row.
Lewis Moody captains England in their second Pool B clash as team manager Martin Johnson makes nine changes to the starting line-up.
England (v Georgia, Dunedin, Sunday 7am UK time)
15 Ben Foden (Northampton Saints)
14 Chris Ashton (Northampton Saints)
13 Manusamoa Tuilagi (Leicester Tigers)
12 Shontayne Hape (London Irish)
11 Delon Armitage (London Irish)
10 Toby Flood (Leicester Tigers
9 Ben Youngs (Leicester Tigers)
1 Matt Stevens (Saracens)
2 Dylan Hartley (Northampton Saints)
3 Dan Cole (Leicester Tigers)
4 Simon Shaw (Unattached)
5 Tom Palmer (Stade Francais)
6 Tom Wood (Northampton Saints)
7 Lewis Moody (Bath Rugby, capt)
8 Nick Easter (Harlequins)
16 Steve Thompson (London Wasps)
17 Alex Corbisiero (London Irish)
18 Tom Croft (Leicester Tigers)
19 James Haskell (Ricoh Black Rams)
20 Joe Simpson (London Wasps)
21 Jonny Wilkinson (Toulon)
22 Matt Banahan (Bath Rugby)
Leicester wing Horacio Agulla retains his place in the Argentina side to face Romania on Saturday, Alesana Tuilagi plays for Samoa against Wales on Sunday and Martin Castrogiovanni is among the Italy replacements against Russia on Tuesday.