The young Canaries suffered their heaviest defeat of the FA Premier Academy League season when they were hammered by the second-placed Saints at Staplewood.
Third-placed City were two goals down before the interval as Corby Moore struck after 11 minutes and Sam Hoskins after 26 minutes.
Lloyd Isgrove made it 3-0 with a goal 10 minutes into the second half, and James Ward-Prowse scored the fourth five minutes later.
A late penalty by Jake Sinclair wrapped up victory for Southampton.
City complete their programme with an away match at Watford on Saturday (11am).
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