There was little festive cheer to be found at Fratton Park as Pompey were beaten by struggling MK Dons.
They created the better chances before the break, but trailed to Bradley Johnson’s close-range header.
Josh Koroma had an effort controversially ruled out in the second half and Jack Tucker struck at the other end to condemn the Blues to a first home defeat since the end of January.
Danny Cowley made three changes from the side that were beaten on the road at Wycombe a fortnight earlier.
Denver Hume was handed a first League One start of the season, while there were also spots for Reeco Hackett and Josh Koroma.
Sean Raggett, Dane Scarlett and Ronan Curtis were the men to make way, with the trio all dropping to the bench.
Pompey came charging out of the blocks and had two chances to break the deadlock in quick succession.
A long throw from Marlon Pack caused chaos in the box and Denver Hume’s volleyed effort was spilled by Jamie Cumming, leading to an almighty scramble before the keeper could gather.
Then, just moments later, Koroma’s curler was parried by the stopper and the ball flew agonisingly out of reach for Owen Dale.
But the visitors began to keep possession well, passing the ball around nicely, without being able to carve out any openings.
And the Blues then started to regain control, leading to another couple of opportunities to take the lead.
A right-sided free-kick from Clark Robertson caught everyone out and the ball bounced off the top of the crossbar before being cleared behind.
The resulting corner was eventually worked to Koroma, whose cleanly-struck 20-yard effort had to be parried away by Cumming.
But instead it was MK Dons who went ahead with their first decent chance of the contest on 34 minutes.
A corner was worked to Conor Grant and he delivered a sumptuous cross that was nodded home by Johnson from just a couple of yards out.
Pompey tried to hit back before the break, but Pack could only glance a header over from Robertson’s corner.
Half Time: Pompey 0 MK Dons 1
The hosts looked bright immediately after the restart and were probing away in search of an equaliser.
Dale did whip a dangerous left-footed delivery into the mixer, but Koroma could not make a clean connection.
Pompey thought they had drawn level on 55 minutes, as Koroma raced onto Jay Mingi’s deflected pass and fired home.
The flag was instantly raised for offside, drawing ire from the home side, who complained that the ball had come off Dons defender Warren O’Hora.
Referee Samuel Barrott ignored their appeals, however, with the angry reactions earning bookings for Hackett and Cowley.
The visitors almost rubbed salt into the wound moments later and Josh Griffiths used his legs to deny Mo Eisa before O’Hora blazed the loose ball over.
Pompey were living dangerously, though, with Griffiths coming to the rescue again after Grant was sent racing through on goal.
But it was only a brief respite and Grant was left in space on the edge of the box to meet a corner, with his scuffed effort finding Tucker, who bundled the ball over the line.
Cowley responded with a triple substitution, as Mingi, Hume and Colby Bishop made way for Joe Morrell, Scarlett and Joe Pigott.
There was another attacking change soon after, with Michael Jacobs brought on to replace Michael Morrison.
Pompey were certainly committing plenty of men forward, although a stretching Scarlett could not quite get on the end of Koroma’s teasing centre.
And although they kept battling right until the end, the Blues were unable to find a route back into the contest.
Pompey (3-4-1-2): Griffiths; Morrison (Jacobs 75), Robertson (c), Ogilvie; Dale, Mingi (Morrell 68), Pack, Hume (Scarlett 68); Hackett; Bishop (Pigott 68), Koroma (Curtis 85)
Booked: Hackett, Dale, Ogilvie
Subs not used: Oluwayemi, Raggett
MK Dons (3-4-3): Cumming; Tucker, O’Hora (c), Jules; Watson, McEachran, Johnson, Harvie; Grant (Robson 87), Eisa, Holland (Barry 81)
Goals: Johnson 34, Tucker 64
Booked: Jules
Subs not used: Ravizzoli, Lawrence, Devoy, Dennis, Grigg
Referee: Samuel Barrott
Attendance: 17,426 (236 away fans)