Portsmouth overpowered nine-man Blackburn as Kanu scored twice on his debut after coming on as a substitute.
Kanu made an impressive debut for Portsmouth
Pompey were ahead at the break after Svetoslav Todorov tapped in from a cross by Benjamin Mwaruwari, who pounced on Lucas Neill's mistake.
Kanu headed in the home side's second and third goals but missed out on a hat-trick when his penalty was saved.
Both Neill and Andy Todd were sent off for the visitors, ironically after they both were guilty of fouls on Kanu.
Kanu's introduction by manager Harry Redknapp proved a masterstroke.
Within two minutes of coming on, the Nigerian had found the net for his new club to put Portsmouth in total control.
Lurking at the far post, he rose superbly to guide a header past Brad Friedel after being picked out by Gary O'Neil's cross.
After tempting Neill into a rash challenge that earned him a second yellow card, Kanu scored again from another O'Neil cross.
But the former Arsenal striker could not make it three goals after being fouled in the area by Todd, who was unlucky to be dismissed.
Friedel saved the spot-kick but could not save Blackburn from a poor start to the season.
It took until December last season for Portsmouth to win a home game.
But on the evidence of this display, Redknapp's side are unlikely to be mired in a second successive relegation fight.
Mwaruwari was one of Redknapp's first signings on his return to Fratton Park and his strength unsettled the visitors in the first half.
Robbie Savage certainly felt the Zimbabwe forward's power following an aerial collision that left the Welshman dazed.
Mwaruwari might have given Portsmouth an early lead when he went close with a powerful shot.
But it was fitting he should play a part in his side's opening goal.
Neill misjudged a long punt forward from Linvoy Primus allowing Mwaruwari to cross for Todorov to sidefoot home.
Portsmouth might have had a second soon after, but Friedel blocked a powerful header from Sol Campbell, another debutant.
Campbell showed his worth in his own box when he slid in to deny Jason Roberts a goalscoring opportunity.
Blackburn found it hard work in attack as Roberts and Benni McCarthy laboured to forge a striking relationship.
With the game still goalless, McCarthy created a moment of panic when his lob bamboozled the Portsmouth defence.
The visitors also threatened David James in the Pompey goal with a series of set-pieces at the start of the second half, but the new signing stood up to the test.
Portsmouth striker Svetoslav Todorov told the club website:
"It was nice to score the first goal, but, you know, I'm just doing my job.
"It's a great win for us and the fans. It's just an unbelievable start to the season. I don't think we could have asked for more than a 3-0 win.
"Sol Campbell, Linvoy Primus, Dejan Stefanovic and Glen Johnson were good."
Blackburn boss Mark Hughes told his club's website:
"Maybe some of them tried to ease themselves into the match and when you do that, it becomes difficult.
"But we pick ourselves up, we can't dwell on this, we've 37 games to come.
"It is poor start from our point of view, but I think you'll see a different performance on Wednesday."
Portsmouth: James, Johnson, Primus, Campbell, Stefanovic, O'Neil, Pedro Mendes, Davis, Taylor, Mwaruwari (Thompson 87), Todorov (Kanu 59).
Subs Not Used: Jordan, Hughes, Pamarot.
Booked: Taylor, Stefanovic.
Goals: Todorov 26, Kanu 62, 84.
Blackburn: Friedel, Mokoena, Neill, Todd, Gray, Bentley (Emerton 69), Savage, Reid, Pedersen, McCarthy (Kuqi 82), Roberts.
Subs Not Used: Brown, Jeffers, Gallagher.
Sent Off: Neill (65), Todd (90).
Ref: A Wiley (Staffordshire).