A second-half comeback by Andy Awford's academy side made it three pre-season wins from three.
After wins over Brighton and Aldershot, Pompey were too strong for Wycombe at Bisham Abbey.
Goals by Ashley Harris (pictured) and Jack Maloney in a five-minute spell at the start of the second half earned the Blues a lead they rarely looked like surrendering.
In doing so Pompey condemned Wycombe to their first pre-season defeat in six matches.
That hadn't looked the likely scenario after 15 minutes when Wycombe went ahead, Josh Scowten racing clear to coolly beat the advancing Matt Gledhill.
The visitors came under the cosh throughout the half but managed to survive. Ollie Taylor put a half volley over the bar, Scowton headed weakly over when in space and Taylor again skewed wide with only Gledhill to beat after Romano Redley had sent a powerful cross into the box.
But 10 changes at half-time saw Pompey emerge a transformed side.
And it was a superb goal on 52 minutes that got them on level terms when Harris rifled an unstoppable 30-yard effort past Max Ingram.
Four minutes later and Pompey were ahead when Kane Cook's cross from the left was met by the head of Maloney.
The home side rarely threatened afterwards and Chinedu Vine might have put the game beyond doubt for the Blues only for his drive to be turned over by Ingram.
Awford said: “It was an improvement on the Aldershot game on Tuesday. We’ve worked hard in training and some of that showed.
“Above all else it was a victory, which can only be good for confidence.
“There are still things we need to go back and work on. But I'm pleased with the result and some of the things that came off.”
Pompey: Gledhill (trialist 46), Wheeler (Fitzharris 46), Butler (K. Cook 46), Colson (Burns 46), Webster (Warren 46), Grant, Jennings (Maloney 46), Higgins (Harris 46), Antelmi (Kinchen 46), Branford (Awford 46), E.Cook (Vine 46)