Nadir Ciftci gave Guy Whittingham's side a sixth minute lead at Westleigh Park and James Hurst doubled their lead on 17 minutes.
However, the hosts were reduced to ten men just two minutes later when Danijel Subotic was shown a straight red card for spitting at Blues defender Dan Preston.
Akwasi Asante pulled a goal back for Malky Thomson's side in the 73rd minute but despite Blues piling on the pressure in the latter stages Portsmouth held on to take all three points.
Portsmouth Res: Stewart; Tallack (Tsovolos 80), Ryan, Wilkinson, Mantyla; Hurst, Stockford, Goddard, Nlundulu; Ciftci (Koroma 68 (Walshe 78)), Subotic. Subs not used: O’Brien, Bennett.
Blues Res: Doyle; Ozturk, Kerr, Preston, Murphy; Gombala, Carsley (Fleet 80), Sammons, Rowe; Ntambwe, Asante.Subs not used: Daniels, Hutchinson.