Gianluca Festa, playing his last game for the club, put them ahead in the first half after his cross took a deflection.
Leading scorer Svetoslav Todorov then grabbed a sensational hat-trick in a ten-minute spell after the break before Steve Stone riffled a superb shot into the top corner to round off a wonderful day for Pompey.
In front of 7,000 travelling fans Harry Redknapp's men showed just why they were a cut above the rest after playing Bradford City off the park.
They can now look forward to a new life in the Premiership while Bantams boss Nicky Law must be hoping he can rebuild his squad with a small budget.
City, desperate to end a recent run which has seen them lose five out of their last six matches, took the game by the scruff of the net in the opening exchanges.
After only two minutes they almost stunned the visitors when Andy Gray bent a low free kick just past Shaka Hislop's left-hand post.
Linvoy Primus cut out a dangerous pass from Claus Jorgensen to deny Gray moments later. Robert Molenaar then headed over the bar following a cross by Simon Francis before Hislop went down low to his right to smother Ben Muirhead's deflected shotPortsmouth gradually imposed themselves on the game after a slow start, creating their first opportunity on 15 minutes. Stone cut inside Mark Bower on the right and played the ball across the box only for Nigel Quashie to let himself down with an awful shot which sailed over the bar.
Stone himself went close with an angled shot which crept past Aidan Davision's far post.
Pompey broke the deadlock after 20 minutes when Festa's low cross appeared to come off a City defender and beat Davison at his near post.
That was hard on City who were almost punished again a few moments later when Molenaar's pass back to Davison fell short. Yakubu Ayegbeni raced onto the ball but Davison spared Molanaar's blushes with a fine block at point-blank range.
Molanaar could then have levelled for City but his downward header from a Francis corner lacked power and did not trouble Hislop.
Once again City were let of the hook when Ayegbeni was left totally unmarked after Stone's cross cut City open. The Nigerian did well to reach the ball at full stretch but could not keep it on target.
Ben Muirhead tested Hislop with a well-struck shot for City before Quashie wasted another golden chance at the other end after Ayegbeni set him up with a fine cutback.
Three minutes after the break, Portsmouth doubled their lead. Todorov and Stone played a one-two inside the box before the Bulgarian ran through the static City defence before coolly slotting the ball into the bottom left-hand corner from close range.
Portsmouth made it 3-0 three minutes later. Paul Merson broke into the City half and fed the ball to Ayegbeni who whipped over a hanging cross to the far post. Todorov gathered the ball and thumped it past Davision's near post.
Todorov then completed his stunning hat-trick from the penalty spot after David Wetherall sent him crashing in the box.
Gus Uhlenbeek almost pulled one back for City with a terrific drive that crashed off the post.
Young striker Danny Forrest was denied when his close-range shot was blocked by substitute keeper Yoshikatsu Kawaguchi.
But it was only a matter of time before Pompey seized control and they grabbed their fifth goal and the best of the game in the 69th minute. Stone unleashed a superb strike from the edge of the box which sailed into the top left-hand corner of the net.