Pompey Academy secured a 3-3 draw at table-topping Oxford – but should probably have claimed all three points.
They broke the deadlock when Freddie Read sent a free-kick into the bottom corner and the advantage was doubled before the break.
Stan Bridgman drove into the box and was fouled by the United keeper, with Leon Maloney tucking away the spot-kick.
But a defensive mix-up allowed Kyran Lofthouse to reduce the hosts’ deficit, while Freddie Niblet then drew them level.
Alfie Stanley (pictured) restored Pompey’s lead with a neat finish following some clever build-up play from Maloney.
The game finished all square, however, after Leon Pitman allowed Slavi Spasov’s shot to squirm under his body and into the net.
Academy manager Mark Kelly said: “We had talked about coming down from the FA Youth Cup game at Fratton Park on Wednesday and making sure our heads were right.
“So I was pleased to see us find good patterns in the opening stages and we began to dominate possession all over the park.
"Youth development is all about making those mistakes and growing from them."
“We were two goals up at the break and looking to keep that momentum, knowing our opponents – who had won eight of their 10 league games this season – would throw everything at us.
“Their threat was pretty route one and they got one back when Ethan Robb went to defend a cross and our keeper also came out for the ball. But he didn’t give a shout and the ball was flicked on for their lad to score.
“We continued to play good football, though, and Alfie created some decent chances for himself, only for Oxford to equalise.
“Then we went ahead again and Haji missed a header from about three yards out that would have wrapped things up for us.
“Instead, a cross has come into the back post, which Liam Kelly and one of their players have both bravely gone for, with the ball spinning up.
“Leon should have just smothered it, but I think he’s tried to scoop it up ready to throw back out and it’s ended up going through his legs.
“He was devastated and it’s a hard lesson about communicating with his back four and keeping those concentration levels high, but youth development is all about making those mistakes and growing from them.
“I also felt we tried to get defending over with too quickly. By that I mean it’s sometimes better to stand off and be patient, rather than dive in and give away silly free-kicks.
“But it was an excellent all-round display from us and the boys are disappointed because in free play, we were in total control.”
Pompey: Pitman; Kavanagh, Robb, Mnoga, Kelly; Read, Bridgman; Maloney, Whiting (Bruce 76), Flint (Bell 60); Stanley