Debutant Adrian Segecic was the hero, netting 38 minutes into his debut, having following up with a left-footed shot after Colby Bishop one-on-one was stopped.
The Australian, along with man-of-the-match Callum Lang, were absolute pests with their energy and drive throughout to stretch the home defence.
Pompey were challenged defensively late on – and always with Oxford’s long throws – but they stood firm to claim victory. And here are our playing ratings...
9. Florian Bianchini - 5
(Replaced by Minhyeok Yang on 66 mins) Started in place of Murphy on the left wing yet didn’t quite come off. Should have done far better with a first-half chance struck straight at the keeper, while was sloppy at times, yet work-rate was very good. Photo: Portsmouth FC
10. Callum Lang - 9 - MOM
(Replaced by Terry Devlin on 80 mins) Asked to play on the right and was simply unplayable as he destroyed Oxford. They had no answer to his energy, while the drive on the counter-attack is something the Blues never had with Matt Ritchie. Photo: Steve Bailey
11. Adrian Segecic - 8
(Replaced by Thomas Waddingham on 90 mins) What a stunning debut. Following an eye-catching pre-season, was rewarded with his Pompey competitive debut and what a performance. Featuring as the number 10, his energy and work-rate was phenomenal. Capped off with the opener, having followed up after Bishop’s one-on-one was saved. Photo: Simon Roe
12. Colby Bishop - 7
Mousinho’s great bluff was that Bishop was fit after all, while also captaining the side. Should have done better with the one-on-one which Segecic followed up to score from the rebound, but led the line superbly. Photo: Paul Phelan