Pompey slipped to their third consecutive defeat with a single-goal loss to Norwich at the Canaries’ Colney training base.
The hosts took the lead after just five minutes when Jack Werndly netted from close range after Ryan Oakley had flicked on Matt Bell’s corner.
Pompey’s best chance to equalise came on 36 minutes, but Alex Grant’s strike crashed against the crossbar.
Director of youth operations Paul Smalley said: “It was a narrow defeat but the performance was disappointing and well below what we expect of the players at this level. Their goal, for example, was scored because of some sloppy marking,
“The pitch was conducive to quick, attacking play and we were able to break quickly and create a couple of good chances early in the game.
“But we found it difficult to penetrate Norwich’s defence and did not retain the ball well enough.
“Tom Fry stepped up from the under-16 side to play in goal and he excelled, making some smart saves and distributing the ball well.
“The consistency of our under-18 side is proving to be a concern – the level of performance in the last two games has been miles apart.
“This is a paramount part of the players’ education but learning does take time and they will all continue to receive support and guidance – both on and off the pitch – in order for them to progress.”
Pompey: Fry; Tallack, Bennett, Magri, Grant; Seeley (Fitzharris 58), Tsovolos, Stockford (c) (Colson 58), Butler; Jennings (Harris 63), Walshe
Sub not used: Gledhill
Norwich: Matthews, Barker, Gordon, Florence (Dobbs 80), Jones, Habergham, Oakley, Ball (c), Werndly, Loza (Kelly 46), Dawkin
Subs not used: Gunn, Simons
There was better news for Pompey’s under-16 side, who drew 3-3 at Norwich.