Pete Gregory’s late goal could not help Pompey avoid defeat against Charlton at Sparrows Lane.
The 18-year-old (pictured) – who has made two substitute appearances for the first team this season – struck on 89 minutes.
But earlier goals from Charlton’s Tosan Popo and Ade Azeez meant it was the Londoners who claimed all three points.
Director of youth operations Paul Smalley said: “We were resilient and professional in the first half and deservedly went in level at the break. But in the second half we made a couple of mistakes and were punished accordingly.
“We kept pushing, however, and were rewarded when Pete Gregory scored a fine individual effort after a spell on the sidelines recovering from illness.
“We tried to find an equaliser and created some good chances, but despite our effort we ran out of time.
“The players are showing signs that they understand the importance of their responsibilities at different stages of the game. They’re beginning to perform consistently at the levels we expect.
“But this is still a time of learning – especially for the new year one scholars. It does take time to adjust to the daily training and education.
“All the young scholars are relishing the challenge of learning, working and developing as a group.
“They accept that mistakes are part of this process and that improving themselves is paramount to their learning.”
Pompey: Gledhill; Tallack, Ryan, Magri, Grant (Butler 60); Gregory, Stockford (c), Tsovolos (Harris 72), Colson, Seeley (Jennings 63); Walshe
Subs not used: Bennett, Fitzharris
Charlton: Hall; Ajayi, Osborne, Cousins (Fox 60), Carter; Azeez, Morris, Warren (c), Harriot (Jordan 85); Popo, Pigott (Willer 60)
Subs not used: Gougit, Poyet
There was better news for Pompey’s under-16 side who won 2-0 at Charlton with coaches Neil Lyne and John Perkins expressing their happiness at the improvement of the players since the beginning of the season.