A late own-goal saw Pompey Women narrowly defeated in a south coast derby at Fratton Park.
It was an even contest for much of the night and the home side had opportunities to secure victory against their title-chasing opponents.
But, with the seconds ticking down, skipper Danielle Rowe unfortunately found her own net to seal the points for Southampton.
Jay Sadler made two changes from the side that were beaten by the same opponents in the FA Cup at the weekend.
Jazz Younger and Rosie McDonnell both returned to the starting line-up, with Cherelle Khassal and Freya Jones making way.
The first half was an extremely cagey affair, with neither side creating much in the way of clear-cut openings.
There were spells of attacking pressure from both teams, but they all too often broke down before the action reached the final third.
Dani Lane hit a shot wide for the hosts, while Sammy Quayle had to nod a dangerous corner behind at the other end.
A surging run from Lane then livened things up and when Hayley Bridge delivered the ball into the box, it was nodded away.
Pompey’s best chance came when Shannon Albuery stole possession from Shelly Provan and fed Quayle, who spun and fired past the post.
There was soon an opportunity for the visitors, but after a neat passage of passing play, Georgie Freeland could only send her shot into the arms of Hannah Haughton.
Half Time: Pompey 0 Southampton 0
It was Southampton who were first to threaten once the action restarted and Haughton got down well to beat away an Ella Pusey effort.
Bridge then sent in a dangerous delivery at the other end and Caitlin Morris did well to get there in front of Albuery to clear.
Sadler made his first switch to freshen things up on the hour mark, with Bridge making way for Tamsin de Bunsen.
Quayle and Albuery then swapped a series of neat passes down the right, but the former took a heavy touch, allowing Kayla Rendell to come off her line and deal with the danger.
A couple of de Bunsen corners soon caused problems, with the first beaten behind by Rendell and the second narrowly evading the head of Albuery.
It was proving to be a more open affair as the conclusion neared and Haughton dived to her right to keep out Alisha Ware’s curler.
McDonnell then made a superb challenge to win back possession and find Albuery, who could not find enough power to properly trouble Rendell.
Sadler’s final roll of the dice saw Lane and Albuery withdrawn, as Jones and Jade Widdows were given a late chance to impress.
But it was Southampton who finally broke the deadlock on 84 minutes – and in extremely fortunate fashion.
Haughton had done well to keep out Lucia Kendall’s strike, but when the ball was sent back into the mixer, Rowe got her legs in a tangle and sent it into her own net.
The visitors might have strengthened their advantage moments late, with Haughton doing well to deny Katie Rood after the substitute raced through on goal.
Another de Bunsen corner was unconvincingly dealt with as the seconds ticked down and despite Pompey committing players forward, they could not find a leveller.
Pompey (3-1-4-2): Haughton; Rowe (c), Younger, Gane; Gotch; Bridge (de Bunsen 60), Rowbotham, Lane (F.Jones 80), McDonnell; Albuery (Widdows 80), Quayle
Booked: Gane
Subs not used: Tonks, Cleeve
Southampton (3-4-1-2): Rendell; Morris, Rafferty, Parnell; Mott, Kendall, Rutherford, Provan (c); Watling (Rood 70); Freeland (Ware 70), Pusey (Morris 70)
Goals: Rowe 84 (og)
Subs not used: Luce, Williams
Referee: Sophie Dennington
Attendance: 1,450