Pompey surrendered their unbeaten league record as they fell to a 2-0 loss to struggling Gillingham.
Kenny Jackett’s men were punished for a weak first-half display, as they slipped to their first League One defeat to a team who’d not won a game since August 11.
The Gills hadn’t tasted success in 10 games but deserved their two-goal lead at the break, with Pompey creating little.
The visitors then withstood a second-half onslaught from the Blues in front of a crowd of 18,158
The only solace for the Blues was Peterborough’s home loss to Barnsley meant they are still three points clear at the head of the table.
The opener came in the 26th minute with a moment of quality from Tom Eaves, as he juggled the ball from Max Ehmer’s header and smashed an unstoppable volley past Craig MacGillivray.
Pompey lacked penetration and quality in their crossing in the first 45 minutes, with Ben Close’s 20-yarder being deflected over by Barry Fuller the best of it in the 43rd minute.
And they were punished for woeful defending two minutes into stoppage-time as Dean Parrett’s corner went through a sea of bodies and was smashed home by Alex Lacey at the back post.
Pompey upped their game after the restart, with David Wheeler and Ben Thompson on for Close and Gareth Evans.
It was all pressure from the home side, but they were nearly undone on the break as Gillingham broke three on one, but Brandon Hanlan strayed carelessly offside.
Brett Pitman’s header wasn’t too far wide in the 60th minute as the pressure continued from the Blues.
Then Jamal Lowe’s effort was deflected wide from a few yards out, as appeals for a foul on Nathan Thompson in the box were ignored by the referee.
Luke O’Neill delivered an important saving header to deny the lurking Pitman from Brown’s cross with 20 minutes left.
Curtis’ curling 20-yarder was tipped over with 20 minutes left as Oli Hawkins replaced Nathan Thompson.
And then there was no blue shirt to tap in from Pitman’s header back across the face of goal from Ben Thompson’s cross.
The fourth official indicated four minutes of stoppage-time, but Pompey never looked like getting back into the game.