Greg Halford scored a 113th minute winner against his former club to send Cardiff City into round 2 of the Carabao Cup.
Click here for video highlights
The draw will be made on Thursday evening after the Bury v Sunderland fixture. Cardiff are seeded so will be drawn against a Championship club that finished in the lower half of the table last season or one of the teams still in the competition from League 1 or League 2.
Portsmouth were gifted a first half lead when Sean Morrison acrobatically volleyed into his own net. A half time rollicking from Neil Warnock and the introduction of Nathaniel Mendez-Laing brought the Bluebirds level in the 48th minute. Mendez-Laing making no mistake a the far post after Matt Kennedy's cross was diverted into his path by Lee Tomlin.
The game ended 1 - 1 after 90 minutes and in extra time Halford finished smartly from 16 yards to win the game for City.
City produced the better chances with Manga hitting the bar, Hoilett forcing a great save from Luke McGee, Matt Kennedy almost dinking one over the keeper, Ibrahim Meite firing wide and Danny ward heading a couple of chances straight at the keeper.
Pompey had their moments and looked a dcent side who ran out of steam and were beaten by the better side in the end.
Report from PA Sport
Cardiff needed extra-time to beat 2008 FA Cup final opponents Portsmouth 2-1 and reach the second round of the Carabao Cup.
Pompey had won the last cup meeting between the two sides on the biggest stage of all and looked as if they might repeat that triumph when Bluebirds captain Sean Morrison scored a 32nd-minute own goal.
But substitute Nathaniel Mendez-Laing equalised before Greg Halford's 113th-minute strike prevented a penalty shoot-out.
Cardiff started brightly with Matthew Kennedy probing down the right and Danny Ward's shot deflected wide.
But Portsmouth gradually got a foothold and the impressive Kyle Bennett twice tried his luck from distance without locating the target.
Kennedy created the clearest chance of the opening half-hour but Ward could not generate enough power on the header and Luke McGee comfortably collected in the Pompey goal.
Cardiff, however, were behind moments later as Morrison failed to deal with Kal Naismith's cross and diverted the ball past a helpless Brian Murphy.
Naismith soon fell under Bruno Manga's challenge and demanded a penalty but referee Stephen Martin waved play on.
Cardiff showed more intent after the break and were almost level within seconds when McGee pushed Manga's header on to the crossbar.
But Cardiff were level two minutes later when Kennedy burst down the left and the ball fell to Mendez-Laing to open his Bluebirds account following his summer move from Rochdale.
Murphy remained alert to deny Gareth Evans and Danny Rose and force extra time and the decisive goal came when Halford met Junior Hoilett's corner and beat McGee.
Cardiff: Murphy; Halford, Morrison (Capt), Manga, Richards; Kennedy (Hoilett 87), O'Keefe, Damour (Ralls 102), Pilkington (Mendez-Laing 46); Tomlin (Meite 97); Ward.
Subs Not Used: Etheridge(gk), Peltier, Coxe.
Portsmouth: McGee; Talbot, Whatmough, Burgess, Haunstrap (Close 106); Evans, Rose, May, Bennett (Baker 98); Pitman (Capt), Naismith (Kabamba 65).
Subs Not Used: Bass(gk), Davies, Main, Chaplin.
Scorers -
Cardiff: Mendez-Laing 48, Halford 113
Portsmouth: Morrison o.g 32
Yellow Cards -
Cardiff: Murphy 45
Referee: Stephen Martin (Staffs)
Attendance: 6,592