Pompey Academy were beaten 5-2 at Swindon to suffer a second successive Youth Alliance League defeat.
But they dominated the opening stages of the contest and went ahead through a goal from Harvey Rew (pictured).
Swindon punished some poor defensive play, however, to roar into a 4-1 lead and after Seok Jae Lee had reduced the deficit, the hosts wrapped things up by scoring a fifth.
Professional development phase coach Liam Daish said: “It was a strange afternoon because it was probably the best I’d seen us start a game this season.
“We played really well for the first 20-25 minutes of the contest and deservedly took the lead through Harvey.
"There were some positives to take from the match, but sloppy errors and not defending set-plays well enough has cost us"
“But individual mistakes and goals from corners either side of the break meant we went from dominating to being 3-1 behind.
“It all came from nothing and that was a period that really rocked us, while it obviously gave Swindon the momentum.
“There were two more goals that came from corners and so it’s clearly something that we do need to address.
“The lads kept fighting, though, and we had a real go at them, with a really nice effort from Seok Jae pulling one back.
“There were some positives to take from the match, but sloppy errors and not defending set-plays well enough has cost us.”
Pompey: Manderson; Setters, Cadman, Rew, Hughes; Jewitt-White, Bell; Dawson (Bridgman 65), Lee, Brook; Gifford (Greenough 81)