Emannuel Adebayor struck a second-half hat-trick as Arsenal piled more misery on relegated Derby at Pride Park.
A ludicrous Darren Moore mistake let Nicklas Bendtner fire in the first before Jay McEveley poked in to level.
Robin van Persie chested a cross down and lashed home and then Adebayor tapped in at the back post.
Robert Earnshaw slotted in for Derby, but Theo Walcott scored a fine solo goal before Adebayor slid in a cross and then rolled home in stoppage time.
Derby's supporters have seen it all before this season, but after a promising opening it was still a remarkable collapse.
With Arsenal all-but guaranteed to finish third and Derby relegated many weeks ago, there was nothing of great significance riding on the game.
But the home side, who are still four points adrift of Sunderland's tally of 15 in the 2005/06 season - until now the worst by a Premier League team - made an impressive start which surprised the Gunners.
They nearly took the lead when Mile Sterjovski's 20-yard shot was heavily deflected by Alex Song and, with Lucasz Fabianski - making his first league start for the Gunners - wrong-footed, the ball dropped inches wide.
But Derby's season has been a catalogue of mistakes and after 24 minutes Moore stupidly gave the ball away to Van Persie, who played in Bendtner to fire under Roy Carroll.
Derby did not deserve to be behind and after Van Persie amazingly fired over from point-blank range, they got themselves back on level terms.
Robbie Savage swung over a free-kick from the left and after McEveley mis-timed a header, he kept his cool when the ball landed at his feet to poke in from four yards.
After a rare moment of joy for the locals at Pride Park this season, it was pretty much all Arsenal for the remainder of the game and within eight minutes they took a lead they were not to relinquish.
Kolo Toure chipped a ball into the box and as Moore embarrassingly stopped and appealed for offside, Van Persie took the ball down on his chest and lashed clinically into the roof of the net.
An injury meant Van Persie was replaced at half-time by Adebayor and the Togo striker immediately threatened to run amok as Derby's defence completely disappeared.
Toure twice burst into the box and shot over, the second effort after a majestic backheel from Cesc Fabregas set him up.
Bendtner struck a sweet half-volley just over from the edge of the box, before Adebayor raced through and was denied a goal by a brilliant Carroll save with his left foot.
Shortly after, Adebayor got on the scoresheet when Walcott raced past Alan Stubbs and his cross was deflected on by Emmanuel Eboue for the big striker to tap-in at the back post.
It was becoming a procession, with Arsenal's fans singing 'ole' with every successful pass as Walcott went clean through only to curl wide.
Derby brought on Earnshaw and he pulled it back to 3-2 when he neatly collected Andy Todd's pass and slotted past the advancing Fabianski.
But Walcott emphatically curled into the far corner after cutting in from the left for a brilliant solo goal and then Adebayor converted Gael Clichy's cross from the left to bag a fifth for Arsenal.
He wrapped it up in injury time with his 30th goal of the season and his second treble of the campaign against the hapless Rams when he ran around Carroll and rolled the ball with consummate ease into an empty net.