Pompey saw their run of good form come to an end with defeat to in-form Barnsley on a chilly night in South Yorkshire.
They were left with an uphill challenge after James Norwood and Nicky Cadden both stuck in the early stages at Oakwell.
Colby Bishop raised hopes of a comeback by heading home shortly after the restart, but they were quickly dashed by Devante Cole’s finish at the other end.
John Mousinho made a single change from the side that battled to victory at Cambridge at the weekend.
Tom Lowery was handed a first start since mid-September, with Michael Jacobs dropping to the bench.
The home side came charging out of the blocks and after taking advantage of a fortunate ricochet, Herbie Kane teed-up Adam Phillips for a shot that was saved by Matt Macey.
There was some neat passing play from Pompey at the other end, but it ended with Connor Ogilvie seeing his effort blocked.
But Barnsley were looking more likely to break the deadlock and a loose pass in midfield saw them do exactly that on 17 minutes.
Phillips intercepted the ball and surged forward, drawing defenders to him before laying it across for Norwood to stroke into the bottom corner.
And the advantage was doubled thanks to a fine strike soon after, with Cadden cutting across from the right and finding the net from the edge of the box.
It might have got even worse for the Blues, but Sean Raggett managed to get in the way of Cole’s attempt.
Harry Isted had enjoyed a comfortable evening at the other end and his first piece of action was a regulation save when Dane Scarlett tried to convert Joe Rafferty’s cross.
The visitors did start to improve going forward towards the end of the first half, but were unable to turn their possession into any meaningful chances.
And the Tykes almost added a third goal just before the break, as Phillips burst forward and drilled in a low shot that was turned around the post by Macey.
Half Time: Barnsley 2 Pompey 0
Pompey started the second half brightly, passing the ball around with more confidence in their search for a breakthrough.
And it soon arrived, as BISHOP laid the ball off for Rafferty, then charged into the box to convert his cross with an emphatic header.
Barnsley soon had a dangerous attack of their own, although Norwood was unable to beat Macey from an acute angle.
Mousinho made a switch just before the hour mark, with Lowery making way for the fresh legs of Jacobs.
Pompey soon found themselves with a two-goal deficit again, however, as Norwood escaped down the right and squared for Cole to slam a close-range shot into the roof of the net.
They were still in charge of possession, but finding more clear-cut openings was proving a harder task.
A quick break up the pitch did see Owen Dale find Ryan Tunnicliffe, whose angled effort was saved by Isted.
Mousinho then made a triple switch, which saw Tunnicliffe, Dale and Scarlett make way for Louis Thompson, Paddy Lane and Joe Pigott.
There was an opportunity when Jacobs collected Ryley Towler’s pass over the top, but after beating one man, his cross was charged down by Mads Andersen.
And although Pompey spent most of the closing stages camped in the Tykes’ half, they were unable to find the goal that would have set up a tense finale.
Barnsley (3-5-2): Isted; B.Thomas, Andersen (c), Kitching; Williams, Phillips (Benson 78), Connell, Kane (L.Thomas 82), Cadden (Larkeche 82); Cole (Watters 69), Norwood (Tedić 69)
Goals: Norwood 17, Cadden 20, Cole 60
Booked: Kitching
Subs not used: Searle, Russell
Pompey (4-3-3): Macey; Rafferty, Raggett (c), Towler, Ogilvie; Lowery (Jacobs 58), Morrell, Tunnicliffe (Thompson 75); Dale (Lane 75), Bishop, Scarlett (Pigott 75)
Goals: Bishop 49
Subs not used: Steward, Bernard, Hackett
Referee: Marc Edwards
Attendance: 10,968 (1,217 Pompey fans)