Pompey Academy enjoyed a more positive trip to Oxford than their first team counterparts, securing a 5-2 victory at Northcourt Road.
They broke the deadlock when pressure from Bradley Lethbridge caused the keeper to drop a cross and Leon Maloney lobbed the ball home.
United equalised, but then conceded a penalty when Matt Mayes’ shot was parried into the net by the hand of a defender.
The referee ruled the goal out and pointed to the spot, showing a red card to the perpetrator. Dan Smith (pictured) then stepped up to score from 12 yards.
Pompey made the most of their numerical advantage, as the ball ricocheted to Mayes and he fired it into the top corner.
The lead was reduced just before the break, but another fine finish from Mayes – this time curled into the bottom corner – got them back on track.
And the points were wrapped up when Smith’s shot was parried clear and Lethbridge reacted quickest to find the net.
Lead professional development phase coach Mikey Harris said: “We were excellent in patches, but also had disappointing moments.
“Going forward in the first half we were very good, although poor defending allowed Oxford to score twice.
"We were excellent in patches, but also had disappointing moments."
“Them going down to 10 men gave us an advantage, but – as often happens – they ended up working even harder to make life difficult for us.
“We had to be patient to break them down and we were strong in the stages just after the interval to increase our lead.
“But I said to the lads at the end I was disappointed because we just dropped off in the final 20 minutes.
“You could say we were 5-2 up and ask why that’s a problem. Well, the standards we set have to be high as possible.
“We scored some good goals and got the win, however, so there are plenty of positives for us to take from the game.”
Pompey: Collins; Chandler, Brooks, Casey, Dandy; Smith, Read, Maloney, Johnston (Flint 62); Mayes, Lethbridge (Whiting 55)