Pompey suffered late heartbreak at Nottingham Forest as two goals condemned them to a 2-1 defeat.
The Blues looked on course for a welcome victory after Kanu put Pompey ahead in the first half.
But an Ibrahima Sonko own goal three minutes from time levelled matters.
And worse was to come for the Blues when Marcus Tudgay bagged Forest's winner four minutes into injury-time.
In a disciplined first-half display, Steve Cotterill's side looked set to end Forest's long unbeaten home record.
Kanu showed fine skill and composure to keep his head and round the goalkeeper to finish well after David Nugent put him through on goal.
Forest, however, had other ideas and got on top after the break as Pompey sat back to defend.
Nathan Tyson clipped the crossbar for the home side, but it was a succession of corners and high balls into the box that turned the screw as the game wore on.
Cotterill attempted to see the game out, throwing on Hermann Hreidarsson in a five-man defence but it allowed Forest to attack almost at will.
With just three minutes remaining, Sonko - who had turned in an otherwise fine display - stuck out a leg attempting to clear Lewis McGugan's cross and wrong-footed Jamie Ashdown as the equaliser bobbled into the net.
While that was hard enough to take, it got even worse for Pompey as Forest scented blood and pressed for the winner in stoppage time.
Once again, it was another high ball into the box and Tudgay was on hand to flick his header beyond Ashdown to deliver the knouckout blow deep into stoppage time for a sickening blow to Pompey.