Nadir Belhadj (right) celebrates the winner that came from his cross
Substitute Kanu's faint touch from a Nadir Belhadj corner gave Portsmouth a vital home win over Bolton.
Minutes after replacing David Nugent, Kanu stole in between Jlloyd Samuel and goalkeeper Jussi Jaaskelainen to steer the ball into the net.
Portsmouth had dominated the first half, with Glen Johnson, in an unusual midfield role, going close to breaking the deadlock on three occasions.
Bolton's best chance, a Johan Elmander strike, was well saved by David James.
But Gary Megson's side, who began the match in the more secure position of the two teams, rarely looked interested in going for all three points.
Portsmouth, on the other hand, would have been plunged into uncertainty again with another defeat. But this well-deserved win for Paul Hart's men more or less dispelled the threat of relegation.
Pompey players 'superb' - Hart
It was an interesting first half, especially for 24-year-old England international Johnson, whose return from suspension saw him find a series of attacking opportunities.
The full-back was elevated from his usual defensive role to a position on the right of a five-man midfield, with Peter Crouch the lone man up front.
With Younes Kaboul playing an industrious role directly behind him, Johnson frequently found himself free to drift inside and even towards the left side of the field as Bolton's defenders struggled to track his movements.
Having already featured in a number of his team's attacks, Johnson collected a ball in the centre circle on 26 minutes and surged upfield, firing in a strong shot from the edge of the area which forced a good save from Jaaskelainen.
Not long afterwards he really should have scored when Niko Kranjcar, skipping down the left, evaded the attentions of two Bolton defenders to release a telling cross.
Johnson was unmarked when receiving the ball, but side-footed his shot weakly straight at the goalkeeper.
If that was Johnson's best chance, he came closest to scoring when a loose ball dropped kindly at his feet inside the area. His shot was struck across the goal and Jaaskelainen's outstretched leap was enough to touch the ball onto the post.
There was still time for Sean Davis to scuff a shot from close range before half-time came, and for all Portsmouth's endeavours it was frustrating for the home fans that the deadlock remained unbroken.
Bolton had produced some disjointed football, perhaps unsettled by the early loss of Ricardo Gardner with a left ankle problem.
His replacement, Fabrice Muamba, was virtually anonymous and there was only one serious chance for Bolton when Elmander broke free on a counter-attack to force James into a fine save to his right.
The visitors provided much stiffer resistance in the second half, but continued to offer limited threat going forward.
As a result, the match entered a tedious phase, although referee Phil Dowd was kept busy, most notably when he booked unused Bolton substitute Nicky Hunt as he spoke to team-mates from the touchline.
Megson criticises 'pathetic' goal
Portsmouth switched to 4-4-2 as Kanu replaced Nugent, but they lost the creative impetus of Kranjcar when he was stretchered off the field after being fouled by Gavin McCann.
Ironically, the enforced substitution - which saw Belhadj join the fray - paid instant dividends as moments later the Algerian's wickedly inswinging corner delivered from the right-hand corner flag resulted in the game's only goal.
Bolton were left to reflect on the woeful defending that allowed Kanu to score, however. First McCann missed his header, then Samuel and Jaaskelainen - the latter making his only error of the game - were left rooted to the spot as Kanu nudged the ball into the net.
Portsmouth manager Paul Hart:
"I didn't really see what happened for the goal but we'll take it. I'm told Kanu has claimed it but it doesn't matter to me who scores as long as it is us and I thought we deserved it today.
"Bolton have a way of playing that makes them difficult to play against but I think you have to give our players credit even though we didn't dominate in the second half as much as in the first half."
Bolton boss Gary Megson:
"We were poor and Pompey were not that much better than us. We've got to show a big improvement on this even though three of our last five matches are at home. We are certainly not thinking we are safe yet.
The defending for the corner was very bad, letting it go straight in like that from Belhadj's corner. Did Kanu claim it? Well, he would. I should know, having had him at West Bromwich Albion!"
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.