Kanu came into the side for the injured Joel Ward so Liam Lawrence had to be content with a place on the bench. Scunthorpe packed the midfield and aimed to frustrate Pompey, which they achieved in the first half.
The home side struggled to keep hold of the ball and therefore failed to create many chances. The only real opening came when a misplaced pass led to a counter-attack which ended with David Nugent volleying from long distance but the ball was tipped over the bar by Josh Lillis.
However, the visitors grew into the game and the small group of Scunthorpe fans who had made the long journey down to Fratton Park must have felt hard done when Lee Miller's goal was harshly ruled out for a so-called "push" on Hreidarsson.
The Iron then had Pompey fans hearts skip a beat later in the half when some sloppy defending saw Michael Collins' shot roll agonisingly wide when nobody closed him down.
The home fans were getting frustrated with their team constantly giving the ball away and so started to make their own entertainment with ironic olé chants amongst other strange noises.
But when an attack looked like coming to fruition, there was nobody there to apply the killer touch to put Pompey ahead, so a poor half ended goalless.
As with many games this season, Pompey came out in the second half a much improved team and began to show their superiority to their opposition but not before Collins tested Ashdown with the visitors' only meaningful attempt in the second half.
Neither Aaron Mokoena or Jonathan Hogg could get on the end of David Cotterill's tantalising cross to give Pompey the lead but the deadlock was finally broken when Dave Kitson struck the ball past Lillis from outside the box.
That goal seemed to take the wind out of Scunny's sails as Pompey began to dominate possession and the inevitable second goal came from an unlikely source.
Mokoena lost the ball but it was won back by Hogg who passed it to Kanu who then squared it back for the South African to fire a big deflected shot past Lillis which effectively sealed the points.
I have to admit that I thought we would struggle to win the game after such a frustrating first half. Scunthorpe had a game plan and it was working well enough that had they gone in at the break with the lead, it probably would have been justified.
Then again, I suppose no team keeps five straight clean sheets without a stroke of luck and Pompey certainly got that today. At least they eventually got it together on the pitch, strung some passes together and made the pressure tell in the end.
Special praise should be reserved for the tenacious Jonathan Hogg who was worthy of the sponsors "man of the match" award but David Cotterill has also proved to be a shrewd loan signing and was the main threat tonight.
Finally, I'd like to say kudos to the hardy Scunthorpe fans that made the journey tonight. Hopefully their dedication will be rewarded with Championship football again next season.
As for Pompey, Championship football next season is now surely a certainty.
Pompey Player Ratings
Jamie Ashdown: 7 - One good save.
Ritchie De Laet: 7 - If only we could sign him permanently...
Greg Halford: 6 - Solid if unspectacular.
Ricardo Rocha: 6 - A couple of "sleepy" moments that might have been costly.
Hermann Hreidarsson: 6 - Stayed strong.
Hayden Mullins: N/A - Replaced with Mokoena early on due to injury.
Jonathan Hogg: 7 - Full of energy and tenacity.
David Cotterill: 7 - Provided the main threat.
Kanu: 7 - Started slow but grew into the game.
David Nugent: 6 - Not as effective as in recent games.
Dave Kitson: 6 - Scored but still unconvincing.
Substitutes
Darryl Flahavan
Carl Dickinson (Nugent 84): N/A - Late run out.
Aaron Mokoena (Mullins 22): 7 - Best performance for a while.
Liam Lawrence
Tom Kilbey
Nadir Ciftci (Cotterill 90): N/A - Time wasting switch.