A close-range Craig Mackail-Smith goal just before half time was enough to give Pompey's South Coast rivals Brighton & Hove Albion all three points at Fratton Park in this Championship encounter.
It was a case of 'what might have been' as Liam Lawrence missed a penalty with almost the last kick of the match following a handball, his shot hit the post.
Such a contrast to the joy of Luke Varney's last minute equaliser at The Riverside a week ago.
Pompey made a number of changes from their mid-week defeat against Barnet in the Carling Cup.
Kanu made his first start of the season, Jamie Ashdown replaced Stephen Henderson and Hermann Hreidarrson and Tal Ben Haim returned from international duty.
Liam Lawrence retained the skipper's armband. Dave Kitson was suffering from a groin strain picked up in training on Thursday and dropped to the bench.
With a stiff westerly wind blowing and Fratton Park bathed in sunshine, the match started at a lively pace as would be expected from a local derby, with both teams contributing to some good play.
Pompey created a number of decent half-chances during the first half - Norris, Varney and Mokoena all went close - but were unable to cause the Brighton 'keeper too much concern.
Kanu linked-up the play well from his central position and, as he always does, looked to have just that little bit of extra skill to retain the ball and make good use of it. Sadly, that wasn't always the case with those around him in support.
Unfortunately for Brighton their double goalscorer from the opening weekend of the Championship, Will Buckley, left the play mid-way through the first-half. The reason wasn't clear but he didn't look very well when he came off the pitch. His replacement, Craig Noone, was lively and caused Pompey a number of problems throughout.
Jamie Ashdown was forced in to making one excellent save in the first half, diving away to his left, as Brighton fashioned a shot on goal from long distance following a free kick that clearly had its roots on the training ground.
HT: Portsmouth 0-1 Brighton & Hove Albion
Pompey tried to apply more pressure in the second half and fashioned a number of half-chances, corners and free-kicks. Varney, who ran the channel well on occasions, Hreidarsson and substitute Kitson all had opportunities but couldn't make them count.
Ashdown's main call to action in the second half was to make another excellent save this time from a long-distance Noone shot, he tipped the ball over the cross-bar and into the travelling fans on the Milton End.
Despite expending a lot of effort and energy in the second half Pompey couldn't create any clearcut shots on goal.
One bright spot for Pompey in the second half was the cameo appearance by Australian teenager Ryan Williams. He looked fearless, had enough pace and trickery to get past the defender down the right hand side and most importantly he got crosses in to the box. He looks a good prospect on the brief showings so far.
Nobody can fault the commitment or the workrate of the players to put the opposition under pressure: Mullins, Norris, Lawrence and Varney have that in spades.
But the team also needed to demonstrate far more creativity and for whatever reason there wasn't enough of that on show on Saturday to make a difference.
FT: Portsmouth 0-1 Brighton & Hove Albion
Flag day pictures - South Stand view
Organised by the PFC Conference, Fratton Park put on a colourful and impressive show of flags on Saturday, there were 17,000 in total laid out on home fans' seats. As the pictures show they made an impressive back-drop leading up to kick-off.
Benjani returns to Pompey!
There had been 'sightings' of the Zimbabwean in the crowd reported on Twitter but his signing was still out-of-the-blue.
In his post-match radio interview on BBC Radio Solent, manager Steve Cotterill said he'd spoken to Benjani the night before from the training ground car park and had got him down on the first available flight. He'd trained that morning and had signed a 12 month deal.
Concerns about Benjani's fitness were dismissed by Cotterill who stated that although the Zimbabwean hadn't featured much at Blackburn Rovers he had hardly missed a day's training and was fit.
The announcement certainly lifted the Fratton Park crowd before the match and there is now great anticipation about his second debut for the Club.
Brighton free-kicks in the first half
Second half goalmouth action at The Fratton End
Pompey Free-kick
Not pretty viewing
This was a niggly game at times and the referee, Mr Swarbrick, was a bit whistle happy which didn't help matters.
There were nine yellow cards shown in the match - five of them to Pompey players (Tal Ben Haim, Luke Varney, Dave Kitson, Hermann Hreidarsson and Liam Lawrence).
There were numerous occasions throughout the game where going to ground appeared to be the option of choice for some of the Brighton players.
Brighton got promoted from League One with a reputation for playing good quality, passing football.
Unfortunately, there was too little of that on display during this game and too many antics.
Brighton won't win over many of the neutral pundits playing this way even if they continue to pick up points.
It certainly irked many home fans at Fratton Park as well as the Pompey players who were suckered in to conceding easy fouls.
Call it professional, call it clever, call it what you want it didn't make very pretty viewing and the play became fragmented as a result.
It will be interesting to see how Brighton's away day trips pan out over the season.
The experienced Isreali international was booked early on in this game, his second yellow card of the season. Although he has showed glimpses of what he can do in both league games this season, he's not quite 'at the races' yet and has been found out more than once. There's clearly more to come.
Kitson came on as a second half substitute and was clearly fired-up, probably due in part to his sending-off at The Withdean Stadium in the FA Cup earlier this year. This 'talking to' followed an off the ball incident, he'd already been booked for an earlier challenge.
Last Minute Drama
Portsmouth versus Brighton: Jamie Ashdown, Tal Ben Haim, Aaron Mokoena, Greg Halford, Hermann Hreidarsson, Joel Ward, Hayden Mullins, David Norris, Liam Lawrence, Luke Varney and Kanu. Substitutes: Stephen Henderson, Ricardo Rocha, Ryan Williams, Christian Dailley and Dave Kitson
Attendance: 16,496 boosted by a large vocal away following that filled out the Milton End
Pompey MOTM: the official award went to David Norris, I would have given it to Aaron Mokoena
Next up for Pompey: Reading at Fratton Park on Tuesday 16th August at 7:45PM in the Championship. It's going to another tough encounter, Reading - last season's play-off finalists - won away to Championship big spenders Leicester City on Saturday and despite losing Shane Long to WBA, the Royals still look a decent outfit.
Source for Pompey team, yellow cards and attendance figure: www.portsmouthfc.co.uk
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