City, without a win in their last six games, kicked off desperate for the points which would help them avoid being dragged into a relegation dog-fight.
But they were up against rampant East Midlands neighbours who had arrived at the Walkers Stadium in search of a new club record of 13 away wins in a season.
City had the better of the opening exchanges but had little to show for their endeavours bar an early corner from Danny Tiatto which sparked a scramble close to the Derby goalmouth before the danger was cleared.
Leicester tried several hopeful balls that were knocked up to paceman Elvis Hammond whose speed occasionally threatened to shake the composure of giant Rams centre-back Darren Moore.
But it was County who took the lead in the 23rd minute with a goal heaped in controversy.
Referee Howard Webb incurred the home side's wrath when he failed to award a penalty for what appeared to be a clear offence when, from Tiatto's corner, Moore dragged back Patrick Kisnorbo before hauling him to the ground in a move which would not have looked out of place in a wrestling ring.
Amazingly the South Yorkshire official waved aside stunned City's vehement protests which allowed Derby to rapidly regroup and counter on the break with Giles Barnes feeding Craig Fagan on the left. He beat the advancing Paul Henderson with an angled side-footrf shot driven low into the far corner of the net.
The Foxes gathered themselves and continued to snap away but lacked the cutting edge to inflict any real damage on their confident opponents, a rising shot from Stephen Hughes which failed to hit the target, was their best effort from plenty of possession.
And five minutes before the break it was the Rams who came to doubling their advantage when Darren Currie slipped the ball to Barnes who turned Kisnorbo before firing just wide.
Two minutes after the restart Tiatto almost levelled for Leicester with a 20-yard drive which flew inches over.
The Australian midfielder was proving to be City's most effective player and he was close again when, after robbing Matt Oakley, he surged forward and unleashed another long-range drive which this time whistled wide of a post.
Leicester continued to press and extracted a fine save from Stephen Bywater on 54 minutes when the Derby keeper had to be at full stretch to turn aside Iain Hume's carefully struck 20-yard free-kick.
Little had been seen of Derby's attack in the second half until the 67th minute when David Jones headed wide from Jay McEveley's cross.
But the home side got their just rewards on 68 minutes when the hard-working Jason Jarrett found Fryatt who turned Dean Leacock before slotting calming beyond Bywater from 12 yards.
It was a sweet moment for substitute Fryatt who had been on the pitch for just 13 minutes - the 21-year-old striker's 83rd minute appearance from the bench at Stoke last Saturday being his first piece of action since January.
The referee then gave Moore the benefit of the doubt again when he appeared to hold back Fryatt inside the area.
Derby began to commit more players to attack and went close to recapturing the lead on 82 minutes with Henderson having to dive smartly to his right to smother Fagan's low 20-yard shot.
Four minutes from the end Leicester's Levi Porter found himself free ten yards out and, although he struck his shot well, Bywater showed good reactions to turn the ball aside for a corner which Derby were grateful to clear.