Pompey suffered a first league defeat at Fratton Park since April 2019 after losing 2-1 to Wigan.
They controlled possession and had periods of dominance, but did not do enough to test a nervous-looking Jamie Jones in the visitors’ goal.
And the Latics took advantage to claim all three points, courtesy of a slightly fortunate Lee Evans’ effort and a long-range Tom James free-kick.
Ellis Harrison came off the bench to reduce the deficit late on, but there was not enough time remaining for the Blues to find an equaliser.
Kenny Jackett made two changes from the side that were held to a draw at Rochdale the previous week.
Michael Jacobs was handed a full debut against his former club, while Cam Pring came in at left-back.
Andy Cannon and Lee Brown both dropped to the bench, where they were joined by new arrival Rasmus Nicolaisen.
Former Pompey players Kal Naismith and Viv Solomon-Otabor started for the visitors, but Gary Roberts missed out with a hamstring injury.
The hosts came tearing out of the blocks and created plenty of opportunities in the opening 15 minutes.
An early effort from Jacobs was blocked, while crosses from him and the lively Marcus Harness caused problems for Jones.
A Ronan Curtis delivery from the right – perhaps assisted by the wind – then drifted towards the net and came back off the post.
The ball then ran loose for Harness, who sent it back into the centre, where John Marquis glanced narrowly wide.
Jacobs soon tried to pick out skipper Tom Naylor at the back post, forcing Naismith to head over his own crossbar.
Pring was providing a threat from set-pieces and a couple of corners were nervously dealt with by Jones.
And when Jacobs tried to find Curtis midway through the half, Tom James slid in to intercept and deny the Republic of Ireland international a simple finish.
But the Blues’ dominance began to wane after such a bright opening, allowing their opponents back into the contest.
It still came as somewhat of a surprise when Wigan broke the deadlock – in somewhat fortunate fashion – on 39 minutes.
Craig MacGillivray got down to try to deal with an Alex Perry effort that was blocked by Sean Raggett.
And with the keeper still down on the ground, he was unable to keep the follow-up from Evans finding the net.
It looked like an equaliser might arrive in stoppage-time when Jacobs’ free-kick was nodded back by Jack Whatmough, but Marquis was flagged offside.
Half Time: Pompey 0 Wigan 1
There was a controversial moment early in the second half when Marquis, racing through on goal, was taken down by Nathan Cameron on the edge of the box.
Pompey were demanding a red card for the defender, but referee Antony Coggins would only brandish a yellow.
It was Curtis who stepped up to take the free-kick, but his effort cannoned into the wall and was cleared to safety.
Wigan were next to threaten when Solomon-Otabor broke into the area on the left and rolled a cross-shot narrowly past the post.
The visitors wanted a penalty when Chris Merrie went down in the box, but Coggins immediately waved him back to his feet.
Jackett soon decided the time was right to make his first substitution, with Harness replaced by Harrison.
The Latics were waiting to take a free-kick while that substitution was taking place and that led to their second goal.
James was around 30 yards out and hit a rocket of a shot that flew between MacGillivray’s grasp and the net.
Pompey started to pick up again and they were awarded a free-kick inside the box when Jones picked up Perry’s back-pass.
The Wigan wall were stationed on the line and did their job to keep out Curtis’ fierce drive, while the resulting cross led to a Bryn Morris shot that was blocked.
A final throw of the dice from Jackett saw Jacobs and Morris replaced by Cannon and Ryan Williams on 71 minutes.
Harrison then started an encouraging move and almost finished it, but could not quite get on the end of Curtis’ cross.
The substitute striker was proving a menace and when he collected Williams’ cross and laid the ball off for Marquis, Cameron flung himself into the path of the resulting shot to divert it behind.
Pring took the corner and that found Sean Raggett, whose header clipped the post, as Wigan survived again.
It was Pompey’s most productive period of the game and Williams soon dragged a shot just past the post.
And HARRISON restored some hope on 89 minutes, lashing the ball home after the ball had ricocheted off Marquis and into his park.
But Wigan used up as much time as they could get away with to see out the closing stages and claim the victory.
Pompey (4-2-3-1): MacGillivray; Johnson, Whatmough, Raggett, Pring; Naylor (c), Morris (Cannon 71); Harness (Harrison 58), Jacobs (Williams 71), Curtis; Marquis
Goals: Harrison 89
Subs not used: Turnbull, Nicolaisen, Brown, Close
Wigan (4-2-3-1): Jones; James, Cameron, Fox, Pearce (Gardner 22); Perry, Merrie (Crankshaw 90+2); Naismith, Evans, Solomon-Otabor (Massey 80); Garner (c)
Goals: Evans 39, James 59
Booked: Garner, Cameron
Subs not used: Evans, Long, Obi, Jolley
Referee: Antony Coggins