Pompey Academy produced a late rally, but it was not enough to prevent defeat to Swindon in a nine-goal thriller at Copnor Road.
They got off to a great start and forged ahead in the second minute, with Bradley Lethbridge nodding in a corner from Josh Flint.
But the Robins then took control and Jacob Bancroft, Rhys Wells, Massimo Giamattei, Teo Atik and Luke Haines all struck before the break to leave the hosts heading for a heavy loss.
It was a much improved performance in the second half, although there were only seven minutes remaining when Oscar Johnston (pictured) reduced the arrears.
That sparked a flurry of late goals, with Freddie Read next to strike when he arrived amidst a melee at the near post to convert another Flint corner.
A fierce long-range strike from Lethbridge gave Pompey hope of a comeback, but time ran out before they could score again.
Academy manager Mark Kelly said: “We looked bright and vibrant early on and went ahead with a great header into the corner.
“We might have increased our lead, but Brad missed a simpler chance than the one he scored and Leon Maloney also had a decent opportunity.
"This was stuff we’d be despondent about if it happened to our younger age groups. We’re talking about things they should be able to do."
“But then Josh slipped and Swindon equalised. Then we went from being in total control to making basic defensive mistakes that let in some extremely soft goals.
“It was everything – the distances were wrong, body position was wrong, they were caught watching the ball instead of their man.
“This was stuff we’d be despondent about if it happened to our younger age groups. We’re talking about things they should be able to do.
“The conversation at the break wasn’t a pleasant one and we made three changes. I told them that we’d conceded five goals, but not one had come about through a piece of clever play.
“It was so much better in the second half and we took control again with some good football, while also looking a lot more solid.
“We got three goals in a short space of time near the end and even had more chances, so we could have come away with at least a draw.
“But you can’t give yourself a mountain to climb like we did and expect to get something from the game.
“We score lots of goals, but concede far too many, so it’s clear what we need to work on in the next few weeks.
“I won’t pick anyone out, although there were individual performances that cost us and they know what needs to improve.”
Pompey: Ridley; Mnoga, Robb (Kavanagh 46), Dandy, Flint; Whiting (Teggart 46), Read, Johnston; Maloney, Lethbridge, Stanley (Bridgman 46)