Pompey conceded a late equaliser at Bognor, as they were denied a second successive pre-season victory.
They created plenty of chances and Paddy Lane saw his penalty saved by Ryan Hall early in the second half.
Fellow substitute Joe Morrell did score from the spot, however, and that looked to be enough for the win, only for a trialist to bundle home in the closing stages.
It was the Isthmian League hosts who made the brighter start and Tommy Lee Higgs blazed an early effort over.
The visitors were then caught in possession and when Lucas Pattenden sent a low ball across the face of goal, a sliding Higgs could not quite make a connection at the far post.
But Pompey were soon on the attack themselves and after Harry Jewitt-White’s shot was blocked, a long-range Ryley Towler effort was saved by Hall.
They went even closer after Liam Vincent collected a fine cross-field Tom Lowery pass and hit a low drive that came back off the inside of the post and into the grateful arms of the Rocks keeper.
Jewitt-White then tried to take advantage of the ball running loose in the box, spinning and drawing a stop from Hall.
Anthony Scully – playing through the middle – did find the net after racing onto skipper Marlon Pack’s lofted pass, but was flagged offside.
And when the same player was brought down just outside the area, Jewitt-White bent the free-kick narrowly over.
It was Bognor who had the final say of the first half, though, as Sam Destcroix failed to find the target from close range.
Half Time: Bognor 0 Pompey 0
The visitors fielded a completely different side after the interval, with Morrell and Lane both making their first pre-season outings after an extended break following international duty.
And they soon set about applying pressure on the Bognor defence, who were doing well to repel them.
There was an excellent chance to forge ahead on 56 minutes, however, when Terry Devlin was tripped in the box by Kyle O’Brien.
Referee Dan Austin pointed to the spot, but Lane’s penalty lacked power and was comfortably repelled by Hall.
It was still pretty much one-way traffic and when Jack Sparkes whipped in a cross, Hall made a superb stop to keep out Sam Folarin’s close-range effort.
And they were handed another great opportunity to score when academy forward Folarin was brought down inside the area by a Rocks trialist.
This time it was MORRELL who stepped up to take the penalty and he confidently slammed the ball into the bottom corner.
Pompey took their foot off the accelerator slightly after that and were almost punished, with Josh Oluwayemi diving to his left to keep out a Tom Holland curler.
But Bognor did level from the resulting corner, as a trialist got on the end of the delivery to force the ball home.
Bognor (4-4-2): Hall; Whyte (Holland 73), Douglas (Trialist C 73), Robson (Howick 73), Mason; Pattenden (Trialist B 73), Anderson (O’Brien 54), Davies (c) (Briffa 66), Destcroix (McCormick 66); Higgs (Olaniyan 54), Mather (Trialist A 73)
Goals: Trialist A 87
Sub not used: Hardcastle
Pompey – first half (4-3-3): Norris; Dockerill, Raggett, Towler, Ogilvie; Lowery, Pack (c), Jewitt-White; Mottoh, Scully, Vincent
Pompey – second half (4-3-3): Oluwayemi; Swanson, Mnoga, Shaughnessy, Sparkes; Devlin, Stevenson, Morrell (c); Lane, Folarin, Hume
Goals: Morrell 75 (pen)
Referee: Dan Austin