In the early stages, neither side dominated proceedings, but one man who stood out was Saints forward Leo Scienza.
The 27-year-old Brazilian unsettled the Preston defenders with his direct play and trickery, and just before the half hour mark he forced Daniel Iversen into a smart save, cutting in and curling an effort goal-bound with his right foot.
The away side had a great chance to score 10 minutes before the break as Dobbin was found in space just outside the box, but to the frustration of a team-mate in space out to his left, he opted to shoot, with his effort flying over the bar.
But minutes later he was able to find the net – after an initial effort was saved by Alex McCarthy, Dobbin was in the right place to tap home his third of the season.
Alongside the joyous Preston cheers, St Mary’s then broke out into boos with a large section of the home fans chanting against their owners.
Saints started the second half with more urgency but they still struggled to carve out any clear-cut chances in their pursuit of an equaliser.
Still’s side had their best chance of the game in the 70th minute when Jander curled a right-footed effort towards the top corner that hit the bar.
But the travelling Lilywhites were able to finish the game in style as Frokjaer-Jensen produced a fine finish in injury time to seal the three points for Preston who move into the play-off positions.
The defeat now means that Southampton have lost five times in the Championship this season alongside their six draws and two wins.
