The match appeared to be heading for a 1-1 draw as it entered extra-time, after Joe Morrell had cancelled out Rafa Ramos’ opener for the hosts.
However, in stoppage time, Harry Jewitt-White headed home from close range and then Destiny Ojo raced clear to make it 3-1 moments later in front of a 2,250 Privett Park crowd.
John Mousinho used 21 players, with only Will Norris completing the full 90 minutes, as he made nine substitutions of 64 minutes.
The late finale flattered Pompey, but here are our player ratings...
1. Will Norris - 7
(Replaced by Jordan Archer on 46 mins) Had absolutely nothing to do, not called upon to deal with a single shot. Also rarely involved in distribution, with the majority of the opening 45 minutes taking place in Gosport’s half. Photo: Jason Brown
2. Jordan Williams - 7
(Replaced by Terry Devlin on 46 mins) Regularly provided some driving runs down the right and could have had a couple of assists had Triallist B taken his chances. Always an attacking outlet and encouraging first outing for the Blues. Photo: Portsmouth FC
3. Triallist A (Jamal Baptiste) - 6
(Replaced by Conor Shaughnessy on 46 mins) Struggled with his distribution on a few occasions, with one early pass nowhere near the intended target. Played as the right-sided centre-half and defensively was sound enough. Photo: Jason Brown
4. Ryley Towler - 7
(Replaced by Tom McIntyre on 46 mins) Occupied his usual position as the left-sided centre-half and was very comfortable. Gosport struggled to threaten during the opening half and, as a result, Towler was rarely tested. Photo: Jason Brown