Jazz Younger netted a stoppage-time winner as Pompey came out on top in a seven-goal thriller at Billericay.
Ella Humphrey cancelled out Jess King’s opener before Annie Rolf’s brace gave the Blues a commanding lead at New Lodge.
But a Lucy Jones penalty and King free-kick either side of the break ensured the hosts levelled the National League contest.
And it looked as though the spoils would be shared until Younger popped up in the dying seconds to secure all three points.
Jay Sadler made three changes from the side beaten by Bournemouth in the semi-finals of the Hampshire Cup a fortnight earlier.
Evie Gane, Dani Lane and Sophie Quirk were all restored to the starting line-up, with Nicole Barrett, Taylor Macdonald and Tierney Scott dropping to the bench.
Pompey started brightly and caused plenty of problems in the opening stages, with a Lane header saved by Alex Baker.
But Hannah Haughton then had to be at her best at the other end of the pitch to turn Georgie Morton’s effort around the post.
And Billericay soon took the lead, as Morton teed-up King to burst forward and tuck the ball into the bottom corner.
The Blues looked to hit back immediately, though, and Humphrey nodded just past the post after meeting Ali Hall’s delivery.
HUMPHREY did grab the leveller on 29 minutes, using the outside of her boot to find the net after Quirk had stolen possession and picked her out in the box.
The contest was then flipped on its head straight from kick-off, with ROLF squeezing her shot home under Baker’s dive.
Haughton made sure the lead was maintained with a superb stretching save to keep out Ruby Sealey’s angled strike.
And ROLF then extended the advantage further, making sure she was quickest to the loose ball when Lane’s initial attempt was saved.
But the home side were back in the contest just before the break, as Jones netted from the spot after Younger had been penalised for a trip on King.
They might even have gone in level, with a free-kick from Jones crashing against the underside of the bar and bouncing clear.
Half Time: Billericay 2 Pompey 3
The second half began at the same breathless pace as the first and a long-range curler from Quirk rattled the post.
But Billericay immediately found themselves level, with King’s free-kick flying into the net from the edge of the box.
Pompey set about trying to restore their lead, but the clear-cut chances had suddenly started to dry up.
Quirk did nod a whipped Humphrey cross back into the mixer, but the danger was cleared before a mint-shirted player could react.
The visitors were starting to move through the gears again and Humphrey fired into the side netting before Baker denied Quirk.
Substitute Barrett was then left with just the keeper to beat after good work from Quirk, only to hit her shot over the bar.
But with the seconds ticking away and a draw looking the likely outcome, Danielle Rowe swung in a corner.
That was cleared, but the ball went back to the skipper and her second delivery was headed home by YOUNGER.
Pompey: Haughton; Rowe (c), Younger, Gane, Wild; Lane, Rowbotham (Barrett 73), Rolf; Humphrey (Bell 90+4), Hall (Scott 87), Quirk (Macdonald 90+4)
Sub not used: Harney