Craig Conway broke Pompey hearts with a stoppage-time winner at Cardiff.
Conway struck at the death to hand his high-flying side a 3-2 win.
It looked for all the world that the Blues would get a plucky point - until Conway fired in Peter Whittingham’s quick free-kick after a foul by Benjani.
Pompey withstood a first-half battering from Malky Mackay’s side.
Kenny Miller thrashed in the opener after 15 minutes - but it could easily have been much worse as Stephen Henderson made a string of fine saves.
But Pompey levelled completely against the run of play six minutes before the break as keeper David Marshall spilled Erik Huseklepp’s cross into the path of Marko Futacs, who rolled the ball home.
Huseklepp nearly put his side in front before the interval but Greg Halford made no mistake four minutes after the restart.
Halford was on hand to fire Dave Kitson’s headed pass home on the turn from 10 yards.
Pompey fell asleep for the leveller as Conway crossed for Husdson to head past Henderson after 70 minutes.
It was backs-to-the-walls stuff from then on for the visitors.
The rearguard action looked to have earned a draw, until Pompey again switched off from a free-kick and Conway grabbed the three points for his side.