A wonder strike from Eddie Wakley (pictured) was not enough to stop Pompey Academy from losing 2-1 to Oxford at Furze Lane.
After a goalless first half, it was the visitors who broke the deadlock when Owen James nodded home from a corner.
And United doubled their advantage in similar circumstances moments later, although this time it was Dejon Noel-Williams who converted a set-piece.
Wakley reduced the deficit in fine style on 77 minutes, with a rocket from long-range that crashed in off the underside of the crossbar.
The Blues pushed forward in search of a late leveller, but Oxford were able to hold on to secure all three points.
Academy coach Mikey Harris said: “We played some good stuff with and without the ball, despite the difficult conditions. It was very windy and the pitch wasn’t great.
“We dominated possession and were defensively sound throughout – with the exception of the two corners Oxford scored from.
“It was disappointing to concede twice in quick succession, especially as we’d worked on set-pieces in training the previous day.
“The lads obviously didn’t put what we’d spoken about into practice and that’s clearly something they need to learn from.
“When you’re dominating games, you cannot afford to switch off if the opposition have the chance to put the ball into your box.
“The best part of the game for us was Eddie’s goal, which was an absolute screamer. I’m delighted for him.
“It’s just a shame we didn’t try more shots likes that in the second half when the wind was working in our favour.
“Overall it was a very positive performance for us and it’s just disappointing that we didn’t get the result we all wanted.”
Pompey: Hall; Saidy, Wakley (c), Casey (Dandy 69); Chandler, Brooks, Read, Smith (Scutt 59), McDowell (Hancott 46); Mayes (Bradbury 63), Woodward
Sub not used: Collins