Pompey’s unbeaten run finally came to an end at the 12th time of asking, as they lost to Gillingham at a sodden Fratton Park.
It was a disappointing display from the hosts, although they remain top of the League One table with Peterborough also suffering a home defeat.
A wonder goal from Tom Eaves opened the scoring, while Alex Lacey doubled the advantage in first half stoppage-time.
The Blues looked much brighter after the break, but despite their best efforts, were unable to find a breakthrough.
Kenny Jackett named an unchanged side for the third game in a row following successive wins on the road at Rochdale and Coventry.
The wet and windy conditions were undoubtedly making life tough for both sides in the opening stages.
It was certainly not conducive to any kind of free-flowing contest, although the visitors seemed to adapt better.
A shot from Luke O’Neill took a slight deflection to deceive Craig MacGillivray, with the keeper recovering to push the ball clear.
Then, after Jack Whatmough had cut out Dean Parrett’s low delivery, Mark Byrne’s effort cannoned into his own player.
There was a moment of levity midway through the first half, as a shot from Max Ehmer went out for a throw.
But the Gills were still looking more likely to break the deadlock and Ehmer’s drive was cleared by Whatmough.
The ball came straight back into the box, however, where it was collected by Eaves, who spun and hammered a sumptuous volley into the roof of the net.
Pompey tried to hit back, although their final ball was mostly lacking, with too many passes being overhit.
They did have a decent opportunity just before the break, with Ben Close’s long-range attempt nervously cleared over his own crossbar by Ehmer.
But there was still time for Gillingham to double their advantage – although this goal was more stoppable than the first.
A corner from Parrett made its way through a crowded area and Lacey was left unmarked to turn it home.
Half Time: Pompey 0 Gillingham 2
Jackett made a double switch at the break, with Gareth Evans and Close withdrawn for David Wheeler and Ben Thompson.
There was immediately some more urgency about their play, with an early attempt from Brett Pitman blocked.
Ronan Curtis and Jamal Lowe then both saw shots blocked in quick succession, as the noise from the stands began to rise.
And Gills keeper Tomas Holy was called into action for the first time on 51 minutes, getting down to his left to keep out Lowe’s drive.
It was certainly looking a lot livelier than before the interval, although the ball was not quite landing for the Blues, especially with a series of corners that the visitors managed to scramble clear.
O’Neill then made a vital interjection, just about nipping into nod clear with Pitman waiting to convert Lee Brown’s delivery.
With something special needed, Jackett made an attacking change on 74 minutes, replacing Nathan Thompson with Oli Hawkins.
But when Pitman did well to meet Ben Thompson’s cross and turn the ball back across goal, there was nobody in the centre to meet it.
Gillingham had weathered the storm, though, and saw out the final moments in relative comfort to become the first team this season to inflict a league loss on the Blues.
Pompey (4-2-3-1): MacGillivray; N.Thompson (Hawkins 74), Whatmough, Clarke, Brown; Naylor, Close (B.Thompson 46); Lowe, Evans (Wheeler 46), Curtis; Pitman (c)
Subs not used: McGee, Walkes, Burgess, Mason
Gillingham (4-1-2-1-2): Holy; O’Neill, Ehmer, Zakuani (c), Fuller; Lacey; Byrne, Reilly; Parrett; Hanlan (List 80), Eaves
Goals: Eaves 26, Lacey 45+2
Subs not used: Hadler, Garmston, Simpson, Nasseri, Rees, Parker
Referee: Christopher Sarginson
Attendance: 18,158 (542 away fans)