Tubbs and Wallace on target against 10-man Stags
Pompey secured a third away league victory of the season in their final match on the road at Mansfield.
Their task was made a lot easier when Ritchie Sutton conceded a penalty and was sent off in the opening seconds.
Matt Tubbs converted the spot-kick and Jed Wallace then doubled the advantage with a long-range effort after the interval.
A fine effort from Jack Thomas gave the 10-man hosts some hope, but the Blues held on to secure all three points.
Gary Waddock made three changes from the side beaten by Bury the previous week.
Johnny Ertl was handed a first start in more than three months in defence, while there were returns for Dan Butler at left-back and the fit-again James Dunne in a diamond midfield.
Before kick-off there was an impeccably observed minute's silence to mark the 30th anniversary of the Bradford fire disaster.
Pompey have conceded early on plenty of occasions this season, but it was them celebrating a goal after just 102 seconds.
Wallace played a neat one-two with Tubbs and burst into the area, only to be dragged to the ground by Stags skipper Sutton.
Referee Graham Horwood immediately pointed to the spot and compounded the hosts’ misery by pulling out a red card.
It was TUBBS who stepped up to take the penalty and sent Lenny Pidgeley the wrong way to take his tally for the season to 23 goals.
The rest of the half failed to live up to that frantic opening, however, and both sides were guilty of some sloppy passing.
But the Blues, perhaps unsurprisingly, dominated possession and most of the play was taking place in the hosts’ half.
A slip by Callum Elder did send Craig Westcarr one-on-one with Pidgelely on 25 minutes, though, and the Mansfield keeper made a fine stop to prevent his side from falling further behind.
The busy Wallace then tried an audacious chip from the edge of the box that drifted narrowly over the crossbar.
There were not too many scares at the other end of the pitch, although the Stags did go close to levelling on 36 minutes.
A long throw from Liam Marsden was flicked on by Matt Rhead, but Paul Jones somehow managed to deny Rakish Bingham from point-blank range.
Bingham then flashed a shot wide from long-range during a spell of Mansfield pressure, but the visitors did not otherwise look like relinquishing their lead.
Half Time: Mansfield 0 Pompey 1
The hosts had not offered much before the break, but came roaring from the traps after it and almost grabbed an immediate equaliser.
Jones made another fine save to keep out Junior Brown’s drive and Rhead’s follow-up was blocked by some last-ditch defending.
Pompey were soon on the attack themselves, however, and Dunne fired narrowly over after Wallace and Tubbs had combined well to tee him up.
And they doubled their advantage on 55 minutes when WALLACE tried his luck from long-range, with the ball bouncing over Pidgeley’s dive and nestling into the net.
They almost forged further ahead soon after, but Pidgeley was equal to Butler’s stunning 30-yard volley and tipped the ball over.
However, the Stags suddenly found themselves back in the game on 67 minutes when Thomas curled an exquisite effort past Jones’ grasp.
Pompey went straight up the other end to have a chance of their own, but Westcarr seemed caught in two minds about whether to shoot or find Tubbs and ended up drilling the ball wide of the post.
He did better to pick out Wallace moments later, only for Callum Elder to make a key challenge and the striker then sent a shot narrowly wide as the Blues looked to give themselves a cushion.
Mansfield pushed more men forward as they looked to grab a share of the spoils, but the Blues held on for the victory.
They even had chances to grab a third late on, but Thomas did well to dispossess substitute Conor Chaplin before Pidgeley saved from Danny Hollands.
Mansfield (4-1-4-1): Pidgeley; Marsden (Hearn 62), Tafazolli, Sutton (c), Elder; Fitzpatrick; Bingham (Lambe 46), Clements (McGuire 75), Thomas, Brown; Rhead
Goals: Thomas 67
Sent off: Sutton
Subs not used: Studer, Shires, Heslop, Oliver
Pompey (4-diamond-2): Jones; Devera, Ertl (c), Webster, Butler; Dunne, Close (Shorey 85), Wallace, Hollands; Tubbs (McCallum 88), Westcarr (Chaplin 81)
Goals: Tubbs 2 (pen), Wallace 55
Subs not used: Poke, May, Fogden, Atangana
Referee: Graham Horwood
Attendance: 4,222 (1,091 Pompey fans)