An unstoppable penalty in injury time saw Durham Women claim all three points at Maiden Castle.
Tia Primmer opened the scoring for Portsmouth minutes into the second half, tapping home a loose ball.
But it was Durham who took home the three points, with goals from Beth Hepple and Lucy Watson sealing The Blues’ victory.
Adam Furness lined up with the same starting eleven that lost to Crystal Palace in the Barclays Women’s Super League 2 last weekend.
Durham had a handful of chances in the first half – Abbey Jones came close to breaking the deadlock in the 13th minute, but the goal line scramble was saved by Jess Gray.
Primmer gave the visitors the lead in the 48th minute, finding Megan Hornby’s cross at the back post, poking home at the second attempt.
In the 56th minute, Mollie Lambert clinically poached the ball from Gray, which fell to Hepple who found the back of the net.
Michaela Foster came close to giving Durham the lead in the 79th minute but her header was fired just over the bar.
The decisive moment arrived in stoppage time, a foul on Grace Collinson inside the 18 yard box found Durham awarded a penalty.
Watson converted from the spot in the 94th, firing the ball into the top right corner, securing Durham the win.