Pompey exited the Bristol Street Motors Trophy after losing to AFC Wimbledon at Fratton Park.
They were punished for some sloppy defending as Aron Sasu, Josh Davison and Alex Pearce all scored inside the opening half-an-hour.
Kusini Yengi reduced the deficit for John Mousinho's men before the break, only for Harry Pell to hit back for the Dons.
And although Gavin Whyte then opened his Blues account, Ali Al-Hamadi struck late on to ensue the visitors won 5-2.