Kitson teed up Harper on the right-hand edge of the penalty area, he cut in past a defender and unleashed a sumptuous left-foot curler into the top corner.
The Reading fans exploded into life, knowing that if results stayed the same elsewhere, they would be playing Premier League football next season.
Their team was dominant as Derby continued to produce a performance typical of their season, with mis-placed passes and defensive slip-ups once more the order of the day.
David Jones did force Marcus Hahnemann to parry a low shot away, before Carroll denied Lita for a third time as the interval approached.
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Derby made two changes at half-time but it made no difference whatsoever as Reading pushed forward for the killer second goal - Lita having a shot blocked by Darren Moore.
Just after the hour mark they doubled their advantage, Nicky Shorey's 25-yard shot saved by Carroll and Lita neatly turning the ball goalwards for Kitson to poke home from two yards.
With the game as good as won, Reading fans turned their attentions to their radios, knowing that one Fulham goal at Portsmouth would send them down.
As they nervously awaited news their own display got better as Doyle, just on as a substitute, crossed from the right and was then on hand to prod in from three yards after two Derby defenders failed to clear their lines.
But with 15 minutes remaining, news filtered through that Fulham had scored at Pompey and Reading were suddenly staring into the abyss.
Lita got the goal his display deserved as he bulleted in an injury-time header from Stephen Hunt's right-wing cross, but it was a meaningless goal.
Fulham held on to victory at Fratton Park and Reading were consigned to relegation.
Derby: Carroll, Mears, Moore, Nyatanga, Lewis, Sterjovski (Edworthy 46), Savage (Feilhaber 46), Ghaly, Jones, Villa (Simmons 63), Miller. Subs Not Used: Price, Addison.
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