Pompey Academy began their Merit League One campaign with a 4-2 defeat to MK Dons at Furze Lane.
A Joey Evans hat-trick and David Kasumu strike saw the visitors triumph against a Blues side who finished the game with just 10 players on the pitch.
Pompey had fought back from two goals down to draw level by the break, with Matt Mayes scoring from the spot and Leon Maloney (pictured) firing home.
But the Dons netted two penalties of their own in the second half following a handball by Josh Flint – which saw him shown a red card – and Leon Pitman’s foul.
Professional development phase coach Liam Daish said: “We started fairly well against a big, physical side and then, almost out of nowhere, found ourselves two goals down.
"It wasn’t a particularly bad display from us and on another day we might have won, but errors at the back have cost us."
“There were a couple of defensive lapses. We didn’t track the runner down the right for the first and it allowed them to get a cross in.
“The second came from a culmination of mistakes and we couldn’t deal with a simple ball that should have been cleaned up.
“We got back into the game, though, and Leon took his goal well – he was probably our best performer on the day.
“From that point I thought we looked on top, only for the referee to make a big call in the second half.
“He decided that the handball prevented a goalscoring chance, so not only did we concede a penalty, but we were also left with 10 players.
“We were light on numbers, with a few injuries and the under-16s also in action, so our options were limited.
“It wasn’t a particularly bad display from us and on another day we might have won, but errors at the back have cost us.”
Pompey: Pitman; Dandy, Casey, Hancott; Flint, Johnston, Read, Whiting (Mnoga 74), Maloney; Stanley, Mayes