First the Scot helped the Foxes plunder a sixth minute lead when his cross was deflected home by Matthew Taylor and then after Muzzy Izzet had rattled the crossbar, Dickov put City two up with a left-foot shot from ten yards on 26 minutes.
After the break Portsmouth threatened briefly when Nigel Quashie pulled a goal back before James Scowcroft struck to make the game safe for Leicester.
Determined to send their fans home happy in the last game of the season at the Walkers Stadium, Leicester were quick to threaten and as early as the third minute a half cleared Izzet free-kick fell to Steve Guppy whose 15-yard shot rippled the sidenetting.
City went ahead in the sixth minute courtesy of an own goal by Pompey left-back Taylor.
Dickov latched on to a Marcus Bent flick and held off Arjan De Zeeuw. The Scottish international's cross from the byline then struck the retreating Taylor leaving the wrongfooted Shaka Hislop with no chance.
Galvanised by the early goal Leicester poured forward and almost doubled their lead on 12 minutes when Izzet crashed a 25-yard free-kick against the crossbar.
Portsmouth responded with efforts from Yakubu Ayegbeni and Steve Stone, neither of which possessed the venom to trouble Ian Walker.
On 20 minutes Lomana LuaLua let fly from 30 yards, but his rising shot was always too high.
Hislop then came to his side's rescue when he leaped across his goal to push out Guppy's angled 12-yard shot.
But there was little he could do to stop City's second goal.
Dickov twisted and turned inside the box, but appeared to have lost the ball until Bent prodded it back to Dickov who drove home from 12 yards.
In time added on Izzet demonstrated great skill when a clever flick and shimmy left Portsmouth defenders trailing in his wake. Spotting Hislop off his line he then attempted to beat the keeper with a clever lob from 25 yards but the ball drifted inches wide.
Three minutes after the restart Alexei Smertin tried his luck from 20 yards, but his low shot was just wide of the target.
Moments later the visitors wasted a great chance to reduce the arrears when Stone picked out LuaLua inside the area. His first touch was poor and Walker was able to gather comfortably.
Dickov replied for the home side with a teasing cross which eluded Hislop with Bent just failing to apply the finishing touch at the far post.
LuaLua then run at goal but Nikos Dabizas got back in the nick of time to block his close-range shot.
But Portsmouth weren't going to be denied. On 66 minutes when Matt Heath failed to cut out Yakubu's cross to allow Quashie to beat Walker with an angled shot from 12 yards.
After Jordan Stewart had tested Hislop from 16 yards, City restored their two-goal advantage with a 71st minute goal from James Scowcroft.
Guppy's cross was only half cleared with the ball falling to Dickov whose shot was beaten out by Hislop. With the visitors' defence slow to react Scowcroft was able to follow up and sweep the loose ball home.
Les Ferdinand then fired a free-kick wide and Lilian Nalis shot over from 20 yards as City sought to put the game beyond Pompey.
Four minutes from the end a lapse by the City defence allowed Yakubu a free run on goal, but he was unable to capitalise dragging his shot wide of Walker at the far post.
Man of the Match: Paul Dickov – Another busy display from the Foxes frontman ensured that his side took three points, albeit too late to avoid relegation from the top-flight.