After such an enjoyable FA Cup season, the Final was a disappointing affair although Pompey just about deserved their success.
The game was almost a repeat of Portsmouth's narrow semi-final victory against West Brom when they did not play particularly well but scored just before half-time and held on to their narrow advantage in the second period.
Harry Redknapp's side famously beat Manchester United in the quarter-finals while Cardiff had beaten Barnsley - the conquerors of Liverpool and Chelsea - in the last four and it was the Bluebirds that started the Final confidently.
Dave Jones' side had been looking to repeat their famous FA Cup success of 1927 without the services of former Liverpool striker Robbie Fowler who continues to be sidelined with a hip problem.
Redknapp surprisingly recalled Pedro Mendes to his starting line-up and left Kanu as the lone striker with Jermain Defoe cup-tied and Milan Baros on the substitute's bench.
The underdogs started brightly as they tried to find Paul Parry at every opportunity and the former Hereford United man gave Sol Campbell plenty of problems with his pace.
However, there was a sign of things to come in the 16th minute when Peter Enckelman dropped a straightforward cross that caused Cardiff to endure a few nervy seconds before eventually clearing the danger.
When they finally woke from their slumbers, Pompey almost took a 23rd-minute lead when a superb move ended with Kanu beautifully slipping the ball past Enckleman only to then fire his shot against a post from a tight angle.
Roger Johnson flicked a header narrowly over David James' bar before Portsmouth scored the all-important goal eight minutes before the interval.
John Utaka's dangerous cross was parried by Enckelman straight to the lurking Kanu who forced the ball over the line from close range.
Undeterred, the Bluebirds bounced back well, and when Parry surged into space down the left, his cross was just too far in front of the rampaging Kevin McNaughton to divert the ball towards goal.
On the stroke of half-time, Glenn Loovens thought he had grabbed a spectacular equaliser when he hooked the ball into the net after a mistake by James, but the referee rightly ruled the effort out for handball.
Portsmouth appeared to be strolling to victory at the start of the second half as Sulley Muntari lashed a 25-yard effort over the bar and substitute David Nugent forced Enckleman to make a fine stop with a shot from a very tight angle.
However, Cardiff rallied in the final quarter and pressed hard for an equaliser without ever really creating a clear-cut opening.
Pompey did survive a couple of goalmouth scrambles and Roger Johnson powered another header narrowly off target while Loovens' effort looped over the bar after he had headed the ball into the ground.
But Redknapp's side held on to their narrow lead and can now look forward to a UEFA Cup campaign next season while Cardiff must attempt to improve on a mid-table position in the Championship.